Arc detection and prevention in a power generation system

ABSTRACT

Methods for arc detection in a system including one or more photovoltaic generators, one or more photovoltaic power devices and a system power device and/or a load connectible to the photovoltaic generators and/or the photovoltaic power devices. The methods measure voltage, voltage noise and/or power delivered to the load or system power device. The methods may compare one or more measurements, an aggregation of measurements and/or values estimated from the measurements to one or more thresholds, and upon a comparison indicating a potential arcing condition, an alarm condition may be set. Embodiments include an arrangement of photovoltaic generators and photovoltaic power devices for reduced-impedance voltage loops which may enhance arc-detection capabilities.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part (CIP) application of U.S. application Ser. No. 13/290,528, filed Nov. 7, 2011, which claims priority to United Kingdom Application GB 1018872.0, filed Nov. 9, 2010, all of which are incorporated herein by reference in their entirety.

The present application is a continuation-in-part (CIP) application of U.S. application Ser. No. 15/250,068, filed Aug. 29, 2016, which claims priority to U.S. provisional patent Application Ser. No. 62/318,303, filed Apr. 5, 2016 and to U.S. provisional patent Application Ser. No. 62/341,147, filed May 25, 2016, all of which are incorporated herein by reference in their entirety.

The present application claims priority to U.S. provisional patent Application Ser. No. 62/395,461, filed Sep. 16, 2016, which is incorporated herein by reference in its entirety.

FIELD

The present invention is related to distributed power generation systems and specifically to arc detection and prevention in photovoltaic power generation systems.

BACKGROUND

A distributed photovoltaic power generation system may be variously configured, for example, to incorporate one or more photovoltaic panels mounted in a manner to receive sunlight such as on a roof of a building. An inverter may be connected to the photovoltaic panels. The inverter typically converts the direct current (DC) power from the photovoltaic panels to alternating current (AC) power.

Arcing may occur in switches, circuit breakers, relay contacts, fuses and poor cable terminations. When a circuit is switched off or a bad connection occurs in a connector, an arc discharge may form across the contacts of the connector. An arc discharge is an electrical breakdown of a gas, which produces an ongoing plasma discharge, resulting from a current flowing through a medium such as air, which is normally non-conducting. At the beginning of a disconnection, the separation distance between the two contacts is very small. As a result, the voltage across the air gap between the contacts produces a very large electrical field in terms of volts per millimeter. This large electrical field causes the ignition of an electrical arc between the two sides of the disconnection. If a circuit has enough current and voltage to sustain an arc, the arc can cause damage to equipment such as melting of conductors, destruction of insulation, and fire. The zero crossing of alternating current (AC) power systems may cause an arc not to reignite. A direct current system may be more prone to arcing than AC systems because of the absence of zero crossing in DC power systems.

Electric arcing can have detrimental effects on electric power distribution systems and electronic equipment, and in particular, photovoltaic systems, which are often arranged in a manner that increases the risk of arching. For example, photovoltaic panels often operate at extreme temperatures due to their necessary exposure to the sun. Such conditions cause accelerated deterioration in insulation and other equipment that can lead to exposed wires. Such systems are also exposed to environmental conditions, such as rain, snow, and high humidity. Further, typical residential and/or industrial photovoltaic applications often utilize several panels connected in series to produce high voltage. Exposed conductors with high voltage in wet/humid conditions create an environment in which the probability of arching increases.

This problem of arching raises system maintenance cost and reduces the lifespan of photovoltaic panels, because photovoltaic panels and other related equipment will need to be repaired and/or replaced more frequently. Arching in photovoltaic systems also increases the risk of fire, thereby increasing operating and/or insurance cost on facilities having photovoltaic systems. The net effect of arching in photovoltaic systems is to increase the threshold at which a photovoltaic system becomes cost competitive with nonrenewable sources of energy, such as natural gas, oil, and coal.

BRIEF SUMMARY

As newly described herein, systems and methods are presented to address the problem of arching in photovoltaic systems, thereby reducing the overall cost, and extending the useful lifespan of such systems. The embodiments described herein, therefore, make deployment of photovoltaic systems in residential and industrial application more competitive with nonrenewable energy alternatives.

Methods are provided for arc detection in a photovoltaic panel system, which may include a load connectible to the photovoltaic panel with one or more mechanisms such as a power line, e.g. a DC power line. An exemplary method may measure power delivered to the load and power produced by the photovoltaic panel. These measurements may be analyzed using a suitable technique. One example of a suitable technique includes a comparison to generate, for example, a differential power measurement result. The differential power measurement result may be further analyzed using, for example, one or more static and/or dynamic threshold values. The analysis may trigger, for example, an alarm condition when the differential power measurement results deviate from one or more threshold values, either at an instant in time or over a time period when the signal is integrated or smoothed. One or more of the measurements (e.g., the second measurement), the static and/or dynamic thresholds, and/or the power measurements may be converted to a suitable format and/or modulation scheme and transmitted to a remote location. In one exemplary method, one or more of the foregoing items (e.g., the second measurement) may be modulated and transmitted (e.g., over the DC power line) to a remote location.

According to further aspects, a device for arc detection in a system may include a photovoltaic panel and a load connectible to the photovoltaic panel using, for example, a power line (e.g. a DC power line). In this aspect, the device may be variously configured to include one or more electronic modules adapted for measuring power produced by one or more photovoltaic panels and/or a distributed and/or centralized controller adapted for measuring power delivered to, for example, the load. Aspects may be variously configured to include one or more mechanisms to analyze power associated with the photovoltaic panel and/or power delivered to the load, dynamically and/or statically, in an instantaneous and/or integrated manner. The analysis may be variously configured to include, for example, dynamic and/or static comparisons of an instantaneous and/or integrated signal. Suitable comparisons may or may not include one or more thresholds. The analysis may collect historical data and determine variations from this historical data. Additionally, the analysis may include predetermined threshold values based on prior test data. Based on the dynamic and/or static comparison, one or more of the mechanisms may be operable to detect arcing when the power output of one or more photovoltaic panels is greater than the power delivered to the load.

According to further aspects, a method for arc detection may be performed in a system having, for example, a photovoltaic string and a load connectible to the photovoltaic string using, for example, a DC power line. The method for arc detection measurement may be variously configured, for example, to quantify a value associated with a noise voltage of the load and/or a noise voltage of one or more of the photovoltaic panels in the photovoltaic string. The quantities associated with the various measured noise voltages may be analyzed using a suitable technique. In one technique, a dynamic and/or static comparison is made between the various noise voltages e.g., (the noise voltage of the load compared with the noise voltage of one or more (e.g. all) of the photovoltaic panels in the photovoltaic string) producing a quantitative value such as a differential noise voltage value(s). The differential noise voltage value(s) may then be analyzed either statically and/or dynamically. In one embodiment, the differential noise voltage values(s) may be compared against one or more threshold values, statically and/or dynamically, instantaneously and/or integrated over time and then compared. Where a threshold is utilized, an alarm condition may be triggered where one or more of the aforementioned values exceed a threshold. For example, upon the differential noise voltage result being more than a threshold value then an alarm condition may be set; upon the alarm condition being set, the photovoltaic string may be disconnected. The various parameters discussed above may be analyzed locally and/or transmitted to a remote location. In one embodiment, one or more of the values may be modulated and transmitted over a DC power line. Upon the power of one or more or all of the photovoltaic panels or the power of photovoltaic string(s) being greater than the power as delivered to the load, then an alarm condition is set according to a previously defined static and/or dynamic criterion.

According to further aspects, one of the methods for arc detection may include software and/or circuits for measuring power delivered to the load and/or power produced by the photovoltaic string.

The measurement of the power of the photovoltaic string may be variously configured. In one example, the measurement involves sending instructions to measure the power output of each photovoltaic panel. The power value of each photovoltaic panel may then be transmitted and received. The power value of each photovoltaic panel may be added, thereby giving the second measurement result. The second measurement result may then be subsequently modulated and transmitted over the DC power line.

The load impedance may be changed according to a predetermined value. The power of the photovoltaic string, in this example, may then be measured again, thereby producing a third measurement result of the power of the photovoltaic string. Followed by the power of the load being measured, thereby producing a measurement result of the power of the load. The various measurements may be compared, thereby producing another differential power result. The various differential power results may thereby produce a total differential power result. In this example, upon the total differential power result being more than a threshold value, an alarm condition may be set. Upon the alarm condition being set, the photovoltaic string may be disconnected in the example. The third measurement result may be modulated and transmitted over the DC power line.

In this example, the measuring of the power of the photovoltaic string may involve sending one or more instruction to measure the power of each photovoltaic panel. The power value of each photovoltaic panel may then be transmitted and received. The power value of each photovoltaic panel may be added, thereby giving the third measurement result. The third measurement result may then be subsequently modulated and transmitted over the DC power line.

In a further example, the sending of instructions to measure power in the string may be to a master module connected to one of the panels of the string. Embodiments may also include slave modules respectively connected to other panels of the string, which may be instructed to measure power. Power measurement results may then be transmitted from the slave modules to the master module. The power measurement results may then be received by the master module, added up by the master module to produce a string power result, which may be transmitted to a central and/or distributed controller in this example.

In some embodiments disclosed herein, a plurality of photovoltaic power devices may be configured to measure voltages in a synchronized manner, which may provide increased accuracy of a summed voltage measurement. In some embodiments, both the voltage measurements and the transmission of associated voltage measurements may be synchronized (e.g., time-synchronized, etc.). The voltage measurements may be taken at input and/or at output terminals of photovoltaic generators (e.g., photovoltaic panels, cells, substrings, etc.), in serial or in parallel photovoltaic strings. According to some aspects, the voltage measurements may be retransmitted in response to a transmission error and/or as a redundancy feature, which may prevent transmission errors or may address other issues.

In some embodiments, photovoltaic power devices may feature multiple output voltage terminals. In some embodiments photovoltaic generators and photovoltaic power devices may be coupled together and/or may be arranged to provide a plurality of lower-impedance voltage loops. Designing photovoltaic string to have lower-impedance voltage loops may, in some embodiments, provide certain advantages. These advantages may include increasing a voltage sensor's ability to detect high-frequency voltage components, which may indicate an arcing condition. According to some aspects, a lower-impedance voltage loop may also provide a way of determining a location of an arcing condition.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1a illustrates an example of circuit showing serial arcing.

FIG. 1b illustrates the circuit of FIG. 1a showing an example of parallel or shunt arcing.

FIG. 2 shows a power generation system including an arc detection feature according to an embodiment of the present invention.

FIG. 3 shows a method according to an embodiment of the present invention.

FIG. 4 shows a method according to an embodiment of the present invention.

FIG. 5a shows a power generation circuit according to an embodiment of the present invention.

FIG. 5b shows a method according to an embodiment of the present invention.

FIG. 5c shows a method step shown in FIG. 5b , in greater detail, the step measures power of a string according to an embodiment of the present invention.

FIG. 5d shows a method for serial arc detection, according to another embodiment of the present invention.

FIG. 6a shows an illustrative diagram showing an example flow process in accordance with disclosed aspects.

FIG. 6b shows an illustrative diagram showing an example flow process in accordance with disclosed aspects.

FIG. 6c shows an illustrative diagram showing an example data packet in accordance with disclosed aspects.

FIG. 6d shows an illustrative diagram showing an example flow process in accordance with disclosed aspects.

FIG. 6e shows an illustrative diagram showing an example flow process in accordance with disclosed aspects.

FIG. 6f shows an illustrative diagram showing an example flow process in accordance with disclosed aspects.

FIG. 7a shows an illustrative diagram showing a power generation system including an arc detection feature in accordance with disclosed aspects.

FIG. 7b shows an illustrative diagram showing an example flow process in accordance with disclosed aspects.

FIG. 8a shows an illustrative diagram showing a photovoltaic power device in accordance with disclosed aspects.

FIG. 8b shows an illustrative diagram showing a power generation system including an arc detection feature in accordance with disclosed aspects.

FIG. 8c shows an illustrative diagram showing a power generation system including an arc detection feature in accordance with disclosed aspects.

FIG. 8d shows an illustrative diagram showing an example flow process in accordance with disclosed aspects.

FIG. 9 illustrates a photovoltaic system configuration in accordance with disclosed aspects.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.

Reference is made to FIG. 1a which shows serial arcing 106 in a circuit 10 a according to background art. In FIG. 1a , a direct current (DC) power supply 102 provides power between power lines 104 a and 104 b. Power line 104 b is shown at ground potential. Load 100 connects power line 104 b to power line 104 a. Serial arcing may occur in any part of circuit 10 a in power lines 104 a, 104 b or internally in load 100 or supply 102 for example. A disconnection or poor connection in power line 104 a between point C and point A is shown which causes an instance 106 of serial arcing. Typically, if series arc 106 can be detected, circuit breakers (not shown) located at supply 102 or load 100 can be tripped to prevent continuous serial arcing 106.

Reference is made to FIG. 1b , which shows parallel or shunt arcing 108 in a circuit 10 b according to background art. In circuit 10 b, a direct current (DC) power supply 102 provides power between power lines 104 a and 104 b. Load 100 connects power lines 104 a and 104 b. Parallel arcing may occur in many parts of circuit 10 b, examples may include arcing between the positive of supply 102 and the ground/chassis of supply 102, if power supply cable 104 a/b is a two core cable; arcing may occur between the two cores, or between the positive terminal 104 a and ground 104 b of load 100. Parallel arcing 108 may occur as shown between power line 104 b at point D and high potential on power line 104 a at point C.

Arc noise is approximate to white noise, meaning that the power spectral density is nearly equal throughout the frequency spectrum. Additionally, the amplitude of the arc noise signal has very nearly a Gaussian probability density function. The root mean square (RMS) arc noise voltage signal (V_(n)) is given in equation Eq. 1, as follows: V _(N)=√{square root over (4KTBR)}  Eq. 1,

-   -   where:     -   K=Boltzmann's constant=1.38×10⁻²³ Joules per Kelvin;     -   T=the temperature in degrees Kelvin;     -   B=bandwidth in Hertz (Hz) over which the noise voltage (V_(N))         is measured; and     -   R=resistance (ohms) of a resistor/circuit/load.

Reference is now made to FIG. 2, which shows a power generation system 201 including an arc detection feature according to an embodiment. A photovoltaic panel 200 is preferable connected to an input of a module 202. Multiple panels 200 and multiple modules 202 may be connected together to form a serial string. The serial string may be formed by connecting the outputs of modules 202 in series. Multiple serial strings may be connected in parallel across a load 250. Load 250 may be, for example, a direct current (DC) to alternating current (AC) inverter or DC-to-DC converter. An electronic module 202 may be included to measures the voltage and/or current produced by a panel 200. Module 202 may be capable of indicating the power output of a panel 200. Attached to load 250 may be a controller 204. Controller 204 may be operatively attached to modules 202 via power line communications over DC power lines connecting load 250 to the serial strings and/or by a wireless connection. Controller 204 may be configured to measure via sensor 206, the power received by load 250. Each panel 200 has a chassis, which may be connected to ground. An instance of serial arcing 106 may occur between two panels 200. An instance of parallel arcing 108 may be shown between the positive terminal of a panel 200 and ground of the panel 200.

Reference is now made to FIG. 3, which shows a method 301 according to one embodiment. Method 301 may be configured to detect serial and/or parallel arcing. Central controller 204 may be configured to measure one or more parameters such as the power received by load 250 (step 300). Module 202 may be variously configured such as to measure the power of one or more panels 200 (step 302). Module 202 may be variously configured. In one embodiment, it transmits a datum representing the power measured of the one or more panels 200 via wireless or power line communications to controller 204. Controller 204 calculates the difference between power generated at panel(s) 200 and the power received at load 250 (step 304). In this example, if the difference calculated in step 304 shows that the power generated at panel(s) 200 may be greater than the power received at load 250 (step 306) according to a predefined criteria, an alarm condition of potential arcing may be set (step 308). Otherwise, in this example, the arc detection continues with step 300.

Reference is now made to FIG. 4, which shows an illustrative method 401. Method 401 is a method, which may be utilized for detecting serial and/or parallel arcing. In a method according to this example, central controller 204 measures (step 400) the root mean square (RMS) noise voltage of load 250. Module 202 may then measure (step 402) the root mean square (RMS) noise voltage of one or more panels 200. Module 202 may be configured to transmit a datum representing the RMS noise voltage measured of panel(s) 200 via wireless or power line communications to controller 204.

One or more controllers may be configured to compare the noise voltage at panel(s) 200 with the noise voltage at the load 250 by, for example, calculating the difference between noise voltage measured at panel 200 and the noise voltage measured at load 250 (step 404). In this example, if the difference calculated in step 404 shows that noise voltage measured at panel(s) 200 may be greater than the noise voltage measured at load 250 (step 406) according to one or more predefined criteria, an alarm condition of potential arcing may be set (step 408).

Further to this example, the comparison (step 404) also may involve comparisons of previously stored RMS noise voltage levels of panel§200 and/or load 250 in a memory of controller 204 at various times, for example, the time immediately after installation of power generation system 201. The previously stored RMS noise voltage levels of both panel§ 200 and load 250 are, in this example, in the form of a look-up-table stored in the memory of controller 204. The look-up-table has RMS noise voltage levels of both panel(s) 200 and load 250 at various times of the day, day of the week or time of year for example, which can be compared to presently measured RMS noise voltage levels of both panel(s) 200 and load 250.

In this exemplary example, if the comparison of the measured load 250 RMS noise voltage datum with the measured panel(s) 200 RMS noise voltage datum may be over a certain threshold (step 406) of RMS noise voltage difference an alarm condition of potential arcing may be set (step 408) otherwise arc detection continues with step 400.

Reference is now made to FIG. 5a which shows a power generation circuit 501 a according to an embodiment of the present invention. Power generation circuits 501 a have outputs of panels 200 connected to the input of modules 202. The outputs of panels 200 may be configured to provide a DC power input (P_(IN)) to modules 202. Modules 202 may include direct current (DC-to-DC) switching power converters such as a buck circuit, a boost circuit, a buck-boost circuit, configurable buck-or-boost circuits, a cascaded buck and boost circuit with configurable bypasses to disable the buck or boost stages, or any other DC-DC converter circuit. The output voltage of modules 202 may be labeled as V_(i).

The outputs of modules 202 and module 202 a may be connected in series to form a serial string 520. Two strings 520 may be shown connected in parallel. In one string 520, a situation is shown of an arc voltage (V_(A)) which may be occurring serially in string 520. Load 250 may be a DC to AC inverter. Attached to load 250 may be a central controller 204. Controller 204 optionally measures the voltage (V_(T)) across load 250 as well as the current of load 250 via current sensor 206. Current sensor 206 may be attached to controller 204 and coupled to the power line connection of load 250.

Depending on the solar radiation on panels 200, in a first case, some modules 202 may operate to convert power on the inputs to give fixed output voltages (V_(i)) and the output power of a module 202 that may be dependent on the current flowing in string 520. The current flowing in string 520 may be related to the level of irradiation of panels 200, e.g., the more irradiation, the more current in string 520, and the output power of a module 202 is more.

In a second case, modules 202 may be operating to convert powers on the input to be the same powers on the output; so for example if 200 watts is on the input of a module 202, module 202 may endeavor to have 200 watts on the output. However, because modules 202 may be connected serially in a string 520, the current flowing in string 520 may be the same by virtue of Kirchhoffs law. The current flowing in string 520 being the same means that the output voltage (V_(i)) of a module should vary in order to establish that the power on the output of a module 202 may be the same as the power on the input of a module 202. Therefore, in this example, as string 520 current increases, the output voltage (V_(i)) of modules 202 decreases or as string 520 current decreases, the output voltage (V_(i)) of modules 202 increases to a maximum value. When the output voltage (V_(i)) of modules 202 increases to the maximum value, the second case may be similar to the first case in that the output voltage (V_(i)) may be now effectively fixed.

Modules 202 in string 520 may have a master/slave relationship with one of modules 202 a configured as master and other modules 202 configured as slaves.

Since current may be the same throughout string 520 in this example, master module may be configured to measure current of string 520. Modules 202 optionally measure their output voltage V_(i) so that the total string power may be determined. Output voltages of slave modules 202, in this example, may be measured and communicated by wireless or over power line communications, for instance to master unit 202 a so that a single telemetry from module 202 a to controller 204 may be sufficient to communicate the output power of the string. Master module 202 a in string 520 may be variously configured, such as to communicate with the other slave modules 202 for control of slave modules 202. Master module 202 a, in this example, may be configured to receive a ‘keep alive’ signal from controller 204, which may be conveyed to slave modules 202. The optional ‘keep alive’ signal sent from controller 204 communicated by wireless or over power line communications, may be present or absent. The presence of the ‘keep alive’ signal may cause the continued operation of modules 202 and/or via master module 202 a. The absence of the ‘keep alive’ signal may cause the ceasing of operation of modules 202 and/or via master module 202 a (i.e., current ceases to flow in string 520). Multiple ‘keep alive’ signals each having different frequencies corresponding to each string 520 may be used so that a specific string 520 may be stopped from producing power where there may be a case of arcing whilst other strings 520 continue to produce power.

Reference is now also made to FIG. 5b which shows a method 503 according to an embodiment of the present invention. In step 500, one or more strings 520 power may be measured. In step 502, the load 250 power may be measured using central controller 204 and sensor 206. The measured load power and the measured string powers may be compared in step 504. Steps 500, 502 and 504 may be represented mathematically by Equation Eq. 2 (assuming one string 520) with reference, in this example, to FIG. 5a , as follows: V _(T) I _(L) =ΣP _(IN) −V _(A) [I _(L) ]I _(L) +ΣV _(i) I _(L)  Eq. 2,

-   -   where:     -   V_(A)[I_(L)]=the arc voltage as a function of current I_(L);     -   V_(T)I_(L)=the power of load 250;     -   ΣP_(IN)=the power output of modules 202 when modules 202 may be         operating such that the output voltage (V_(i)) of a module         varies in order to establish that the power on the output of a         module 202 may be the same as the power on the input of a module         202 (P_(IN)); and     -   ΣV_(i)I_(L)=the power output of modules 202 with fixed voltage         outputs (V_(i)) and/or power output of modules 202 (with         variable output voltage V_(i)) when string 520 current decreases         sufficiently such that the output voltage (V_(i)) of modules 202         increases to a maximum output voltage level value. In all cases,         the maximum output voltage level value (V_(i)) and fixed voltage         outputs (V_(i)) may be pre-configured to be the same in power         generation circuit 501 a.

The comparison between string power of string 520 and of the power (V_(T)×I_(L)) delivered to load 250 may be achieved by subtracting the sum of the string 520 power (ΣP_(IN)+ΣV_(i)I_(L)) from the power delivered to load 250 (V_(T)×I_(L)) to produce a difference. If the difference may be less than a pre-defined threshold (step 506), the measurement of power available to string 520 (step 500) and load 250 (step 502) continues. In decision block 506, if the difference may be greater than the previously defined threshold, then an alarm condition may be set and a series arc condition may be occurring. A situation of series arcing typically causes the transmission of a ‘keep alive’ signal to modules 202 from controller 204 to discontinue, which causes modules 202 to shut down. Modules 202 shutting down may be a preferred way to stop series arcing in string 520.

Reference is now made to FIG. 5c which shows method step 500 (shown in FIG. 5b ) in greater detail to measure power of string 502 according to an embodiment of the present invention. Central controller 204 may send instructions (step 550) via power line communications to master module 202 a. Master module 202 a may measure the string 502 current as well as voltage on the output of master module 202 a and/or voltage and current on the input of master module 202 a to give output power and input power of module 202 a respectively. Master module may instruct (step 552) slave modules 202 in string 502 to measure the output voltage and string 502 current and/or the input voltage and current of modules 202 to give output power and input power of modules 202 respectively. Slave modules 202 may then be configured to transmit (step 554) to master module 202 a the input and output powers measured in step 552. Master module 202 a receives (step 556) the transmitted power measurements made in step 554. Master module 202 a then adds up the received power measurements along with the power measurement made by master module 202 a (step 558) according to equation Eq.2. According to equation Eq.2; ΣP_(IN)=the power output of modules 202 when modules 202 may be operating such that the output voltage (V_(i)) of a module varies in order to establish that the power on the output of a module 202 may be the same as the power on the input of a module 202 (P_(IN)); ΣV_(i)I_(L)=the power output of modules 202 with fixed voltage outputs (V_(i)) and/or power output of modules 202 (with variable output voltage V_(i)) when a string 520 current decreases sufficiently such that the output voltage (V_(i)) of modules 202 increases to a maximum output voltage level value. In all cases, the maximum output voltage level value (V_(i)) and fixed voltage outputs (V_(i)) may be pre-configured to be the same in power generation circuit 501 a. The added up power measurements in step 558 may be then transmitted by master module 202 a to central controller 204 (step 560).

Reference is now made to FIG. 5d , which shows a method 505 for serial arc detection, according to another embodiment of the present invention. First differential power result 508 occurs in circuit 501 a, with load current I_(L) now labeled as current I_(I) and with voltage V_(T) across load 250 (as shown in FIG. 5a ). First differential power result 508 may be produced with reference to FIG. 5a and equation Eq.3 (below) as a result of performing method 503 (shown in FIG. 5c ). Eq. 3 is as follows: V _(T) I ₁ =ΣP _(IN) −V _(A) [I ₁ ]I ₁ +ΣV _(i) I ₁  Eq. 3,

-   -   where:     -   V_(A)[I₁]=the arc voltage as a function of current I₁;     -   V_(T)I₁=the power of load 250;     -   ΣP_(IN)=the power output of modules 202 when modules 202 may be         operating such that the output voltage (V_(i)) of a module         varies in order to establish that the power on the output of a         module 202 may be the same as the power on the input of a module         202 (P_(IN)); and     -   ΣV_(i)I_(L)=the power output of modules 202 with fixed voltage         outputs (V_(i)) and/or power output of modules 202 (with         variable output voltage V_(i)) when string 520 current decreases         sufficiently such that the output voltage (V_(i)) of modules 202         increases to a maximum output voltage level value. In all cases,         the maximum output voltage level value (V_(i)) and fixed voltage         outputs (V_(i)) may be pre-configured to be the same in power         generation circuit 501 a.

The impedance of load 250 may be adjusted (step 510) optionally under control of central controller 204. Typically, if load 250 is an inverter, controller 204 adjusts the input impedance of load 250 by variation of a control parameter of the inverter. A change in the input impedance of load 250 causes the voltage across the input of load 250 to change by virtue of Ohm's law. The voltage (V_(T)) as shown in circuit 501 a across load 250 may be therefore made to vary an amount ΔV as a result of the input impedance of load 250 being adjusted. The voltage across load 250 may be now V_(T)+ΔV and the load 250 current (I_(L)) may be now I₂.

A second differential power result 522 may be now produced as a result of performing again method 503 (shown in FIG. 5c ) on the adjusted input impedance of load 250 performed in step 510. Second differential power result 522 may be represented mathematically by equation Eq. 4, as follows: (V _(T) +ΔV)I ₂ =ΣP _(IN) −V _(A) [I ₂ ]I ₂ +ΣV _(i) I ₂  Eq. 4,

-   -   where:     -   V_(A)[I₂]=the arc voltage as a function of current I₂;     -   (V_(T)+ΔV)I₂=the power delivered to load 250;     -   ΣP_(IN)=the power output of modules 202 when modules 202 may be         operating such that the output voltage (V_(i)) of a module         varies in order to establish that the power on the output of a         module 202 may be the same as the power on the input of a module         202 (P_(IN)); and     -   ΣV_(i)I_(L)=the power output of modules 202 with fixed voltage         outputs (V_(i)) and/or power output of modules 202 (with         variable output voltage V_(i)) when string 520 current decreases         sufficiently such that the output voltage (V_(i)) of modules 202         increases to a maximum output voltage level value. In all cases,         the maximum output voltage level value (V_(i)) and fixed voltage         outputs (V_(i)) may be pre-configured to be the same in power         generation circuit 501 a.

The first differential power result 508 may be compared with the second differential power result 522 (step 524), for example, using controller 204 to subtract the first differential power result 508 from the second differential power result 522 to produce a difference. The difference may be expressed by equation Eq. 5, which may be as a result of subtracting equation Eq.3 from equation Eq.4, as follows: V _(T) I ₁−(V _(T) +ΔV)I ₂ =V _(A) [I ₂ ]I ₂ −V _(A) [I ₁ ]I ₁ +ΣV _(i)(I ₁ −I ₂)  Eq. 5

The summed output power (P_(IN)) of each module 202 for circuit 501 a may be thus eliminated.

Equation Eq. 5 may be re-arranged by controller 204 by performing a modulo operator function on equation Eq.5 to obtain an arc coefficient α as shown in equation Eq. 6.

$\begin{matrix} {\frac{{V_{T}I_{1}} - {\left( {V_{T} + {\Delta\; V}} \right)I_{2}}}{\left( {I_{1} - I_{2}} \right)} = {\alpha + {\sum V_{i}}}} & {{Eq}.\mspace{14mu} 6} \end{matrix}$

-   -   where the arc coefficient α is shown in Eq.7

$\begin{matrix} {\alpha = \frac{{{V_{A}\left\lbrack I_{2} \right\rbrack}I_{2}} - {{V_{A}\left\lbrack I_{1} \right\rbrack}I_{1}}}{\left( {I_{1} - I_{2}} \right)}} & {{Eq}.\mspace{14mu} 7} \end{matrix}$

Controller 204, for example, may be configured to calculate coefficient α according to the above formula and measurements. A non-zero value of arc coefficient α shown in equation Eq. 7 causes an alarm condition to be set (step 528) otherwise another first differential power result 508 may be produced (step 503). A situation of series arcing typically causes the ‘keep alive’ signal to be removed by controller 204, causing modules 202 to shut down. Modules 202 shutting down may be a preferred way to stop series arcing in string 520.

Reference is now made to FIG. 6a , which shows a flow process (e.g. a method) 601 showing a flow diagram of detecting an arc in accordance with one or more features described herein. In one or more embodiments, the process 601 illustrated in FIG. 6a and/or one or more steps thereof may be performed by one or more computing devices, such as a controller computing device, which may be similar to or the same as controller 204 of FIG. 2. For example, the computing device (e.g., the controller, etc.) may be and/or include an analog circuit, microprocessor, Digital Signal Processor (DSP), Application-Specific Integrated Circuit (ASIC) and/or a Field Programmable Gate Array (FPGA). The controller may be in communication with one or more modules similar to or the same as modules 202 and may use one or more communication methods such as Power Line Communications (PLC), wireless communications (e.g. cellular communication, WiFi™, ZigBee™, Bluetooth™ or alternative protocols) and/or acoustic communication. In some embodiments, one or more aspects or steps of process 601 may be carried out by a master-module controller, e.g. a controller which may be part of a master module (e.g., module 202 a).

For illustrative, non-limiting purposes, process 601 will be described as carried out by controller 204 which may be in communication with modules 202 (e.g. in communication with modules 202 comprising communication and/or control devices) as shown in and described with respect to FIG. 2. Process 601 may be similarly used with regard to different arrangements of power modules, controllers, and other devices. According to some embodiments, controller 204 may be included in and/or in communication with a device such as a power module (e.g. power modules 202), combiner box, photovoltaic inverter, etc. According to some devices, controller 204 may be connected and/or wirelessly coupled to power modules and/or other PV devices. According to some devices, controller 204 may be a remote server configured for remote control of a PV power system. Any of the disclosed steps of FIG. 6a (and/or associated descriptions herein) may be omitted, be performed in other than the recited other, repeated, and/or combined.

Process 601 may begin at step 602, where a computing device (e.g., the controller 204) may instruct (e.g., via one or more communication methods disclosed herein) a plurality of string-connected modules (e.g. modules 202) to measure one or more electrical parameters. These electrical parameters may be module-based parameters (e.g., a module output voltage V_(i)). In some embodiments, the instruction may indicate a time or a timestamp at which a module may begin measuring the output voltage and/or may indicate a time interval at which a module may begin measuring the output voltage after an event, such as after receiving the instruction from the controller 204.

In some embodiments, the taking of measurements of an electrical parameter may be synchronized, which may be used to facilitate summing of the measured parameters. For example, the controller 204 may send instructions to synchronize voltage measurements, which may be used to determine a total string voltage by summing one or more of the individual time-synched voltage measurements.

In another example, an instruction sent at step 602 may comprise an instruction for a module (e.g., in a serial string of modules) to sample output voltage V_(i) at the instant or right after the instruction is received by a module. According to some aspects, instructions sent at step 602 may travel at speed comparable to the speed of light, i.e., 3·10⁸ m/sec, or at some other speed. As an illustrative numerical example, if communications between the controller 204 and the modules 202 take place at about only one-third of the speed of light (e.g. about 10⁸ m/sec), and a maximum communication-path distance between any two modules 202 of the plurality of string-connected modules 202 is 100 m, the respective points in time at which each respective pair of modules 202 receives the instruction might differ by no more than about

$\frac{100}{10^{8}} = {1\mspace{14mu}\mu\;{s.}}$ If each of the plurality of string-coupled modules 202 immediately measures a voltage upon receiving the instructions, then the plurality of measurements may be considered to be substantially simultaneous (i.e., corresponding to points in time which are close enough for the sum of the measurements to be accurately representative of the total string voltage at a single point in time).

In some embodiments, an instruction sent at step 602 may include information for synchronizing the transmission of measurements, such as voltage measurements taken by the modules 202. For example, the instruction may instruct one or more of the modules 202 of FIG. 5a to measure an output voltage 10 seconds after receiving the instruction, may instruct a first module (e.g. 202 a) to transmit a measured output voltage 1 second (or a corresponding number of clock cycles according to a clock that may be comprised in the module) after measuring the output voltage, may instruct a second module 202 to transmit a measured output voltage two seconds after measuring the output voltage, and so on. In this manner, each of the plurality of modules 202 may measure the module output voltage at substantially the same time, but may transmit the measurement at a different time relative to another module 202, which may decrease the likelihood of simultaneous transmissions and the likelihood of possible loss of data (e.g. dropped data packets).

In some embodiments, an instruction sent at step 602 might not instruct the modules 202 to synchronize measurement transmissions, but may instruct one or more modules 202 to wait a random period of time before transmitting a measurement. If a wide window of time is allowed for the transmissions, the probability of overlapping transmissions may be low. As an illustrative, numerical example, each module 202 may be capable of transmitting a measurement within 100 msec. If forty modules 202 transmit measurements during a 5-minute window, and each module 202 broadcasts a measurement at a random time during the 5-minute window, then with probability of

${{\prod\limits_{i = 0}^{39}\left( {1 - {i \cdot \frac{100\mspace{14mu}{ms}}{{5 \cdot 60}\mspace{14mu} s}}} \right)} = 0.77},$ no two measurement transmissions may overlap and each transmission may be received. According to some aspects, the probability of no two transmissions overlapping may be estimated, determined or calculated by Eq. 8, which follows:

$\begin{matrix} {{p_{no\_ overlap} = {\prod\limits_{i = 0}^{N - 1}\left( {1 - {i \cdot \frac{transmission\_ time}{window\_ size}}} \right)}},} & {{Eq}.\mspace{14mu} 8} \end{matrix}$ where N indicates the number of transmitting modules 202, and the transmission time and window size may be selected to obtain a desired probability of non-overlapping transmissions, with N*transmission_time<=window_size. According to some aspects, a preferred configuration may include transmission_time<<window_size.

It is to be understood that the elements of measurement synchronization disclosed with regard to process 601 may be similarly applied to other methods disclosed herein. For example, one or more steps of method 500 depicted in FIG. 5c may use the measurement and/or transmission synchronization as described with regard to FIG. 6 a.

In some embodiments, step 602 might not be implemented, and each module 202 in a string of modules 202 may independently measure an output voltage measurement without receiving an instruction from the controller 204. For example, each module 202 may measure an output voltage every several minutes (e.g. every minute, every five minutes, or every fifteen minutes, etc.).

In some embodiments, each module 202 may measure a direct current (DC) output voltage and/or an alternating current (AC) output voltage. For example, each module 202 may comprise a DC-to-DC converter outputting a DC output voltage (or other parameter such as current), and each module 202 may measure the output DC voltage. According to some embodiments, each module 202 may comprise a DC-to-AC converter (e.g. an inverter, or a micro-inverter, etc.) outputting an AC output voltage, and each module 202 may measure the output AC voltage (or other parameter such as current).

At step 603, the controller 204 may receive measurements (e.g., output voltage measurements) from one or more of the plurality of modules 202. In some embodiments, each module 202 may transmit a tag (e.g., a unique code, an ID code, etc.) along with a measurement. According to some aspects, the controller 204 may compare each unique tag to a list of tags (e.g., a list held in a non-transitory computer readable memory that may be coupled to and/or included in the controller) to determine whether a voltage measurement has been received from a particular module. According to some aspects, the list of tags may be obtained prior to step 602 (i.e., in a method step not explicitly denoted in FIG. 6a _. For example, the step may include identifying one or more modules of the plurality of modules and storing the unique tag associated with each module.

Optionally, if one or more measurements might not have been properly received by the controller 204, the controller 204 may instruct one or more modules 202 to retransmit a measurement. For example, if a measurement is not received from a first module 202 and from a second module 202, in some embodiments, the controller 204 may instruct all or some of the modules 202 to retransmit measurements, and/or in some embodiments the controller 204 may request retransmission only from the first module 202 and/or the second module 202.

In another embodiment, one or more modules 202 may initially (e.g. in response to step 602) transmit a module output voltage measurement twice, which may provide redundancy and protection against a loss of measurements (e.g., due to overlapping transmission times). For example, in relation to Equation 8 above, if each measurement is transmitted twice, in the event of lost measurements, a probability of both measurements transmitted by a single module 202 to be lost may be very small, increasing the probability of the controller 204 receiving at least one measurement from each module 202.

At step 604, the controller 204 may determine whether one or more of the timestamps associated with the measurements received at step 602 indicate about the same time. For example, the controller 204 may evaluate a timestamp associated with one or more of the received voltage measurements to determine whether the measurements received at step 603 indicate about the same time a respective measurement may have been taken. For example, if two timestamps indicate a small or negligible difference in time (e.g., several milliseconds), the controller 204 may determine that the measurements may have been taken at about the same time. In another example, if two timestamps indicate a large or non-negligible difference in time (e.g., several seconds, tens of seconds or minutes, or larger), the controller 204 may determine the measurements to have been taken at different times (i.e., not at about the same time). If all of the measurements or all the measurements of interest are determined to have been taken at or about the same time, the controller 204 may proceed to step 605, which will be discussed below in more detail. If all of the measurements or all of the measurements of interest are determined to not have been taken at or about the same time, the controller 204 may proceed to step 610 and/or return to step 602.

In some embodiments, before returning to step 602, the controller 204 may execute step 610. At step 610, one or more alternative arc-detection steps and/or methods may be utilized. For example, at step 610, one or more voltage measurements, which may have been received from a plurality of modules 202 and may have been determined to have been measured at different times, may be used by the controller 204 to determine or estimate a corresponding voltage for each module at a particular time (e.g., according to process 650 of FIG. 6e described below in more detail). According to some aspects, the controller 204 may proceed to step 605 and may use the voltage values determined in step 610. According to some aspects, at step 610, the controller 204 may compare the received voltage measurements to previously measured voltage measurements, and may determine that an arcing condition may be present based on one or more module voltages showing a trend indicating an arcing condition (e.g. a rise or fall in a measured voltage over time).

At step 605, the controller 204 carrying out process 601 may calculate a sum of one or more of the output voltage measurements received at step 603, which may be denoted as ΣVi for voltage, but may be denoted as another symbol for other parameters such as current, power, etc. According to some aspects, ΣVi may indicate a voltage (e.g., total voltage) across a string (e.g. 520) comprising a plurality of serially-connected modules 202 or may indicate a voltage across a portion of the string.

At step 606, the controller 204 (or other device or entity) may compare ΣVi to a reference parameter (e.g., voltage, current, power, etc.). For example, the reference may be a single reference voltage or a plurality of reference voltages. In some embodiments, the reference may be a sum of voltages ΣVi obtained from a previous execution of method 601 (e.g., a value saved at step 608, which will be discussed below in more detail). In some embodiments, the reference may be a series of voltages measured over time (e.g. ten values of ΣVi obtained by previous executions of method 601). In some embodiments, the reference may be a voltage measured at a different location in a power generation circuit (e.g. 501 a) and/or in a power generation system (e.g. 201). In one example, the reference may be a voltage measured at the input of load 250 of FIG. 5 a.

At step 607, the controller 204 may determine whether the comparison carried out at step 606 indicates an arcing condition. For example, in some embodiments, the controller 204 may compare ΣVi to a reference voltage measured at the input of load 250, which may be denoted as V_250, and may determine that an arcing condition may be present if Vdiff=ΣVi−V_250>Vthresh, where Vthresh may be selected to be a minimum difference voltage that may indicate an arcing condition. In some embodiments, Vthresh may be about 1 volt. In some embodiments, Vthresh may be smaller or larger than about 1 volt. Referring back to FIG. 2, in case of a series arc 106, a voltage drop across series arc 106 (which may be referred to as Varc) may begin at a low voltage (e.g., several tens or hundreds of millivolts) and over the time, Varc may increase, such as to several volts (e.g., such as to 10 volts, 100 volts, or even higher). According to some aspects, Varc might not be measured by a module 202, but Varc may be reflected by V_250, i.e., the voltage measured at the input of load 250. For example, Varc corresponding to series arc 106 might not be included in a voltage measurement taken by modules 202, but a voltage measurement taken at the input of load 250 may include a component corresponding to Varc. By selecting a suitable Vthresh, series arc 106 may be detected before a dangerous condition arises.

In some embodiments, Vthresh may be selected according to historical data. For example, Vthresh may be selected according to differential voltages measured in power generation systems under one or more arcing conditions. In some embodiments, ΣVi may be compared to previously measured voltages and/or differential voltages. For example, executing method 601 ten times, once every three minutes, may generate ten different ΣVI results and ten differential voltage results Vdiff. If these ten Vdiff results (e.g. Vdiff1, Vdiff2, . . . , Vdiff10) indicate a trend (e.g., a rising differential voltage over a period of time) and a newly obtained Vdiff11 result continues the trend, the controller 204 may determine that an arcing condition may be present.

If the controller 204 determines at step 607 that no arcing condition might be present, the controller 204 may return to step 602 and, after a period of time, restart method 601. In some embodiments, the controller 204 may proceed from step 607 to step 608 and save the calculated values ΣVi and Vdiff to memory for future use, and then proceed from step 608 back to step 602. In some embodiments, the controller 204 may save, at step 608, additional data such as individual measurements received from modules (e.g. modules 202), for future reference and analysis. According to an embodiment, measurements saved at step 608 may be used at steps 653-654 of method 650, depicted in FIG. 6 e.

If the controller 204 determines at step 607 that an arcing condition might be present, the controller 204 may proceed to step 609, and set an alarm condition. Setting an alarm condition may result in various safety protocols taking place.

For example, the controller 204 (or other device) carrying out method 601 may be coupled to a wired and/or to a wireless network(s)/Internet/Intranet, and/or any number of end user device(s) such as a computer, a smart phone, a tablet, and/or other devices such as servers which may be located at a location, such as a network operations center and/or power generation monitoring center. These devices may be utilized to generate a warning to warn of a dangerous condition and/or to take action to degrade or turn off certain portions of power generation circuit 501 a. For example, these warnings can be audio and/or visual. According to some aspects, these warnings may be a beep, a tone, a light, a siren, an LED, or a high lumen LED. These warnings may be located or actuated at a premises, such as in a home, in a building, in a vehicle, in an aircraft, in a solar farm, on a roof, in power generation circuit 501 a, etc. In one example, a warning may be centralized (such as in a server) and/or distributed to end user devices (e.g., computers, smart phones, and/or tablets). The warnings may be shown on displays coupled, attached, and/or embedded into various components of power generation circuit 501 a, such as disconnects, switches, PV cells/arrays, inverters, micro inverters, optimizers, residential current devices, meters, breakers, main, and/or junction boxes, etc. The warnings may be variously coupled to a user's or installer's cell phone and/or other device (e.g., person device, computing device, etc.) to make a user aware of a circuit in a dangerous condition and/or to warn a user when the user may be approaching or in proximity to a circuit in a dangerous condition. The warnings may be coupled to or otherwise associated with GPS coordinates and/or generated in response to a device (e.g., smart phone, tablet, etc.) moving in a location proximate to a hazard condition. The measurements sent by modules 202 and/or the summed measurement ΣVi may be analyzed locally and/or sent to another device for further analysis, storage, and review.

In some embodiments, step 609 may include shutting down power production of a power generation system in response to an arcing condition. According to some aspects, if at step 607, the controller 204 determines that an arcing condition may be present, the controller 204 may repeat one or more steps of process 601, which may reduce the risk of a “false alarm” and/or reduce the frequency of shutting down a power generation system due to one or more inaccurate or unreliable measurements or due to measurement noise. According to some aspects, the control 24 may repeat one or more steps of process 601 more than once. According to some aspects, the execution and/or repetition of the steps of process 601 may occur in rapid succession (e.g., one second apart, several seconds apart, etc.) or may be spaced further apart (e.g., several minutes apart, several hours apart, etc.). In some embodiments, an alarm condition may be set only if two or more executions of method 601 indicate an arcing condition. According to some aspects, the process 601 may end at any time and/or after any step.

In some embodiments, method 601 may be carried out by a controller 204 coupled to multiple PV strings. The controller 204 may carry out method 601 with regard to each PV string (e.g. if ten PV strings are coupled to the controller 204, the controller 204 may execute method 601 ten times every 5 minutes, with each execution of method 601 applied to a different string). In some embodiments where the controller 204 is coupled to multiple PV strings, step 609 may further comprise indicating which string coupled to the controller 204 triggered the alarm condition (i.e. which string may be subject to an arcing condition).

Reference is now made to FIG. 6b , which shows a process according to an embodiment. Process 611 may be carried out by a controller or other computing device, e.g. a device configured to control a module (e.g. a photovoltaic power device such as a DC-DC converter, a DC-AC microinverter, a disconnect switch, monitoring device and similar devices). For example, the computing device (e.g., the controller, etc.) may be and/or include an analog circuit, microprocessor, Digital Signal Processor (DSP), Application-Specific Integrated Circuit (ASIC) and/or a Field Programmable Gate Array (FPGA). The controller may control one or more modules similar to or the same as modules 202 and may use one or more communication methods such as Power Line Communications (PLC), wireless communications (e.g. cellular communication, WiFi™, ZigBee™, Bluetooth™ or alternative protocols) and/or acoustic communication

For illustrative, non-limiting purposes, process 601 will be described as carried out by a controller 804 of FIG. 8a (which may be similar to or the same as controller 204 and will be discussed below in more detail), which may be a feature of power module 802 which may be similar to or the same as modules 202 of FIG. 2. The controller 804 carrying out method 611 may be in communication with a second controller 204 carrying out method 601, e.g. using Power Line Communications (PLC), wireless communications or acoustic communications. For example, method 611 may be carried out by a controller included in a power module, and method 601 may be carried out by a controller included in a PV inverter in electrical communication with the power module. The controller 804 may measure control one or more sensors for measuring electrical parameters associated with the module, such as input and/or output voltage, current, power, solar irradiance and/or temperature, for example, sensor/sensor interface(s) 805 of FIG. 8a which may be similar to or the same as sensor 206 and will be discussed below in more detail). If sensor/sensor interface(s) 805 include a voltage sensor, the voltage sensor may be placed in parallel to detect a voltage at an input or output of, for example module 802 of FIG. 8 a.

At step 612, the controller 804 may receive an instruction (e.g., originating from a second controller 204 carrying out step 602 of method 601) to measure a parameter (e.g., input and/or output voltage, current, power, solar irradiance and/or temperature) of an associated module (e.g., a module 202 of FIG. 2).

At step 613, the controller (e.g. controller 804) may instruct an associated sensor to measure an output voltage of a module (e.g., module 202), and the voltage measurement may be saved to memory (e.g. memory device 809 of FIG. 8a , which will be discussed below in more detail). In some embodiments, the controller 804 may receive an instruction (e.g., at step 612 or at another time) that may indicate a certain time for carrying out one or more aspects of step 613. For example, the instruction received at step 612 may instruct the controller 804 to measure the output voltage at a time (e.g., at 1:00:00 pm), or may instruct the controller to measure the output voltage after a predetermined period of time (e.g., 3 seconds after receiving the instruction).

At step 614, the controller 804 may determine a period of time before the controller 804 instructs communication device 806 transmits the voltage measurement at step 615. In some embodiments, the instruction received at step 612 (or at another time) may indicate a time at which step 615 should be carried out, which may reduce the probability of multiple controllers transmitting simultaneously. For example, the instruction received at step 612 may indicate that the output voltage may be transmitted at 1:00:01 pm (i.e., one second after measuring). In some embodiments, the controller 804 may select a period of time (e.g., a random or pseudo random period of time, etc.) to wait before transmission. For example, the controller 804 may select a random period of time between 1 second and fifteen minutes (e.g., according to a uniform distribution) to wait before transmitting the voltage measurement.

At step 615, the voltage measurement is transmitted to an associated controller (e.g., a controller 204 carrying out method 601). In some embodiments, the voltage measurement may be transmitted along with additional information, for example, an identification (ID) tag associated with the controller and/or a timestamp indicating the time/timestamp (or other description) at which the voltage measurement was obtained. In some embodiments, at step 615, the voltage measurement may be transmitted more than once, which may increase the probability that the measurement will be received at least once by a receiving second controller.

At step 616, the controller 804 may receive an instruction to retransmit a voltage measurement, for example, the controller 804 may retransmit a voltage measurement if a communication may have been lost and/or not received by another component, such as due to a transmission error. If such an instruction is received, the controller 804 may loop back to step 615 and retransmit. If no such instruction is received, the controller 804 may return to step 612 and wait to receive additional instructions to measure output voltage. According to some aspects, the process 611 may end at any time and/or after any step.

Reference is now made to FIG. 6c , which illustrates a data packet 630 according to one or more disclosed aspects. Data packet 630 may comprise one or more elements, such as a sender ID tag 632, a timestamp 633 and one or more measurements 634. The sender ID 632 tag may indicate an identification (e.g., a unique ID) of an associated controller or module sending data packet 630. The measurements 634 may comprise one or more measurements obtained by sensors at a module (e.g. 202 or 802), for example, voltage, current, power, temperature and/or irradiance measured at or near a module (e.g., modules 202). The timestamp 633 may indicate the time at which the measurements 634 were obtained and/or measured. If several measurements were taken at different times, several timestamps 633 may be included for respective measurements. In some embodiments (e.g., in a case where the packet may be received by a device which might not be the intended final recipient), the packet may include a target ID tag 635 corresponding to an intended or subsequent recipient. In some embodiments, the packet may include a header 631 comprising metadata regarding the packet contents and may include a cyclic redundancy check (CRC) portion 636, which may provide increased data integrity.

According to some aspects, data packet 630 may be sent at step 615 of method 611 and/or may be received at step 603 of FIG. 6a . The timestamp 633 of data packet 630 may be read and/or processed (e.g. by a controller 204) at step 604 to verify that data packet 630 was received at about the same time as one or more other data packets. According to some aspects, the data packet 630 may comprise measurements 634 that may be used (e.g. by a controller 204) at step 605 to calculate a sum of voltages (or other parameters) measured by a plurality of modules (e.g. 202).

Reference is now made to FIG. 6d , which illustrates a process for arc detection according one or more disclosed aspects. According to some aspects, step 610 of process 601 may include one or more steps of process 640. Process 640 may be used by a controller (e.g., controller 204) to detect or determine an arcing condition using one or more parameter measurements (e.g., voltage measurements), which might not have been measured and/or obtained at about the same time. For example, one measurement may have been obtained at a first time and a second measurement may have been obtained at a second time.

At step 641, a controller (e.g. 204) carrying out method 640 may evaluate a group of timestamps 633 corresponding to a respective measurement 634 of a group of parameter measurements 634 (e.g., voltage measurements, current measurements, etc.). For example, the controller may read a plurality of timestamps 633 and determine that the timestamps 633 might not be about the same (e.g. the timestamps 633 might indicate a plurality of points in time differing by seconds, tens of seconds, minutes or hours).

At step 642, the controller 204 may select a reference timestamp ts. In some embodiments, the reference timestamp may be one of the group of timestamps 633 (e.g., the earliest timestamp, the latest timestamp, an intermediate timestamp, or the median timestamp, etc.). In some embodiments, the reference timestamp ts might not correspond to one of the group of timestamps 633 (e.g., may be an average of two or more timestamps in the group of time stamps or may be a random time within the range of timestamps).

At step 643, the controller 204 may determine a plurality of voltage estimates, calculations, or approximations corresponding to the measured voltages at the reference timestamp ts. For example, if at step 641 the controller 204 evaluates timestamps t1, t2, t3 and t4 corresponding to the voltages V₁[t1],V₂[t3],V₃[t3] and V₄[t4] (e.g., voltages measured at four different modules 202), at step 643, the controller 204 may determine the voltages {tilde over (V)}₁[ts], {tilde over (V)}₂[ts], {tilde over (V)}₃[ts] and {tilde over (V)}₄[ts] (i.e., the voltages at the four modules 202 at the timestamp ts). According to some aspects, the controller may determine these voltage estimates by interpolation, regression analysis, etc. Aspects of step 643 are discussed below in more detail with respect to FIG. 6 e.

At step 644, the controller (e.g. 204) carrying out method 640 may calculate a sum of the output voltage measurements estimated or determined at step 643, which may be denoted ΣVi. ΣVi may indicate a total voltage across a string (e.g., 520) or portion of a string 520 comprising a plurality of serially-connected modules 202.

Steps 645, 646 and 647 may be similar to or the same as steps 606, 607 and 609, respectively, of process 601, but may instead use a value determined in step 644. Step 648 may be similar to or the same as step 608 of method 601, but may instead use a value determined in step 644. According to some aspects, the process 640 may end at any time and/or after any step.

Reference is now made to FIG. 6e , which illustrates a process for estimating parameters (e.g. voltages) at a particular timestamp, according to an embodiment. Method 650 may be used to estimate or determine voltage drops at a reference timestamp, for example, as step 643 of method 640 depicted in FIG. 6d . At step 651, all voltages to be estimated (e.g., V₁[ts], V₂[ts], etc.) may be initialized by the controller 204 to an “unestimated” state or an “unapproximated” state. For example, the controller 204 may recognize one or more voltages that may be used by the controller 204 in the determination of an arc condition.

At step 652, the controller 204 may select an unestimated voltage V_(i) (e.g., V₁) for estimation.

Estimation may comprise, for example, a direct calculation, probabilistic calculation, lookup and/or reception (e.g. via wired or wireless communication) of an estimated or determined value.

At step 653, the controller 204 may load previously measured or obtained (e.g., measured at step 608 of method 601 in a past execution of method 601) measurements of V_(i). For example, the controller may load k previous measurements of V_(i), where k is a positive integer. In systems where V_(i) may change slowly and/or in a substantially predictable manner, the parameter k may be small, for example, k may be 1, 2 or 3. According to some aspects, an elapsed period of time between the timestamp of the j-th previous voltage measurement and the reference timestamp ts may be referred to, for notational convenience, as Δt_(j), with j being a positive integer less than or equal to k.

At step 654, the controller 204 may determine an approximated voltage V_(i)[ts], with the approximation denoted {tilde over (V)}_(i)[ts]. According to some aspects, the controller 204 may use the previous voltage measurements loaded at step 653 as input to an appropriate estimation algorithm.

In some embodiments, a voltage V_(i) may vary slowly over time, and an estimated voltage at the reference timestamp may be {tilde over (V)}_(i)[ts]=V_(i)[ts−Δt₁], i.e., k=1 and the voltage at the reference timestamp may be determined to be the same as the last measurement. In another embodiment, an estimated voltage at the reference timestamp may be calculated by fitting previous voltage measurements to a linear curve, for example, using the formula:

${{\overset{\sim}{V}}_{i}\lbrack{ts}\rbrack} = {{V_{i}\left\lbrack {{ts} - {\Delta\; t_{1}}} \right\rbrack} + {\frac{{V_{i}\left\lbrack {{ts} - {\Delta\; t_{1}}} \right\rbrack} - {V_{i}\left\lbrack {{\Delta\; t_{1}} - {\Delta\; t_{2}}} \right\rbrack}}{{\Delta\; t_{1}} - {\Delta\; t_{2}}} \cdot \left( {{ts} - {\Delta\; t_{1}}} \right)}}$ i.e., where k=2. In embodiments where V_(i) may change more rapidly or in a more complicated manner, k may be greater than 2, and higher-order polynomials, sophisticated functions such as exponential and/or logarithmic functions, or statistical models may be used to estimate {tilde over (V)}_(i)[ts]. A threshold (e.g., a threshold used at step of method 601 607 or step 646 to determine whether a discrepancy between a sum of voltages and a reference voltage indicates an arcing condition) may be selected according to a statistical error in estimating {tilde over (V)}_(i)[ts]. For example, if {tilde over (V)}_(i)[ts] can be estimated with high accuracy, a small threshold may be used (i.e., even a small discrepancy between a sum of voltages and a reference voltage may trigger an alarm condition indicating arcing). According to some aspects, a greater threshold may be used. According to some aspects, the voltage V_(i) may be marked as “determined,” “estimated,” or “approximated.”

At step 655, the controller 204 may determine whether one or more (or all) voltages V_(i) have been estimated. If all voltages (or the voltages of interest) have been estimated, the controller 204 may proceed to step 656 and provide the estimated voltages V_(i) for further analysis (e.g. to be used by a controller and/or a computing device at step 644 of process 640). If it is determined that one or more voltages (i.e., one or more voltages of interest) might not have been estimated, the process 650 may loop back to step 652. The process 650 may end at any time and/or after any step.

Reference is now made to FIG. 6f , which illustrates a process 660 for detecting an arcing condition according to one or more disclosed aspects. A device (e.g., a controller 204 or some other device) may or might not execute one or more steps of process 660 as part of a different process (e.g., as step 610 of process 601). According to some aspects, a controller (e.g. 204) executing process 660 may detect a potential arcing condition by detecting an uncontrolled trend in measured (e.g., currently measured, previously measured, etc.) parameter (e.g. voltage, current, power and/or temperature) measurements. For illustrative purposes, voltage measurements are used to illustrate an aspect of process 660.

At step 661, the controller 204 may receive (e.g. load from a memory component and/or receive by communication from another device) k (1, 2, 3, etc.) measured voltage measurements (e.g., measured at an input or at an output of a module 202 or at load 250).

At step 662, the controller 204 may attempt to detect a trend in the voltage measurements. For example, the controller 204 may determine whether the voltage measurements show an increase or decrease over time or stay substantially the same. According to some aspects, other trends may be detected using linear regression, non-linear regression, etc. In one example a voltage drop across an arc (e.g., arc 106) may consistently grow over time (e.g., due to melting of conductors, which may increase an arcing air gap and thereby increase the arcing voltage), which may result in a measured voltage (e.g., at a module 202) increasing over time. Changes in arcing voltage, which may be observed over time, may vary according to one or more parameters, including but not limited to a current flowing through the conductor at which the arc may occur, conductor material, temperature and other operational and environmental parameters. The controller (e.g. 204) executing process 660 may be calibrated according to one or more of these parameters, which may be known or determined (e.g., experimentally estimated) according to the location of the component, device, or system performing the process 660.

According to an embodiment, a voltage drop across an arc may be estimated by Eq. 9, which follows: V _(arc)=(V _(c) +d·V _(d))·(1+√{square root over (I ₀ /I)})  Eq. 9 where V_(arc) may be a full arc voltage, V_(c) may be a voltage at an arcing contact point, d may be an arc air gap size, V_(d) may be a parameter relating a voltage drop across the air gap to the size of the air gap d,I may be the current flowing through the arc, and I₀ may be a parameter (e.g., a parameter that may depend on the conductor material). According to some aspects, I may be measured by a module 202 and thereby may be known, and d may grow over time (e.g., due to conductor melting), which may provide a change in measured voltages, which may indicate an arcing condition.

As an illustrative, numerical example, a system may have

${V_{c} = {15\lbrack V\rbrack}},{V_{d} = {5\left\lbrack \frac{V}{mm} \right\rbrack}},{I_{0} = {1\mspace{11mu} A}},{I = {15\mspace{11mu}{A.}}}$ An arc air gap size may grow by 0.1 mm/sec, arc voltage may grow by about 1V every 3 minutes, which may cause a voltage measured at an output of a module 202 to grow by 50 mV every 3 minutes (e.g., in a case where an output impedance of a module 202 comprises about 5% of the total loop impedance “seen” by an arc), or may cause a voltage measured at an input of a module 202 to grow by about 500 mV every 3 minutes (e.g., in a case where the arc is at an input of a module 202, and an input impedance of a module 202 is about 50% of the total loop impedance “seen” by the arc).

It is to be understood that the illustrative values provided in the numerical example above are simply indicative of possible values corresponding to a feasible scenario in one embodiment. The values may vary in alternative systems and embodiments, and the illustrative values used above are not limiting in any way.

At step 663, the controller 204 may determine whether the voltage measurements loaded at step 661 indicate a trend, and if the measurements indicate a trend—whether the trend is controlled. An example of a controlled trend may be a startup condition, e.g., at the start of a day where one or more modules 202 may actively increase an output voltage, to provide increasing power to load 250. Another example of a controlled trend may be a reduced voltage at an input to a module 202 caused by a module 202 executing Maximum Power Point Tracking (MPPT). Because controlled trends may occur during normal system operation, if a controlled trend is detected (e.g., by correlating the trend with commands issued by control devices or with operational changes in modules 202 and/or load 250), the controller 204 may proceed to step 664, which may be similar to or the same as step 608 of method 601, and may save the measurements. If an uncontrolled trend is detected at step 663, the trend may be indicative of an arcing condition (e.g., an uncontrolled arcing condition), and the controller 204 may proceed to step 665, which may be similar to or the same as step 609 of method 601, and may set an alarm condition. According to some aspects, the process 660 may end at any time and/or after any step.

Reference is now made to FIG. 7a , which shows a photovoltaic (PV) generation system 701 according to an illustrative embodiment. PV generation system 701 may comprise a plurality of PV generators. In the illustrative embodiment shown in FIG. 7a , each PV generator may comprise a PV panel 700, which may be similar to or the same as panel 200. In some embodiments, the PV generators may comprise individual PV cells, substrings of PV cells, one or more PV panels and/or PV arrays. In some embodiments, the PV generators may be replaced or complemented by one or more batteries, capacitors, supercapacitors, fuel cells, wind turbines or other power generation or storage sources.

Each PV generator (in the case of FIG. 7a , each panel 700) may be coupled to a power module 702 (e.g., 702 a, 702 b, 702 c and so on, referred to collectively as “modules 702”). According to some aspects, a power module 702 may be similar to or the same as module 202. Each module 702 may comprise input terminals and output terminals, which may be coupled to a panel 700. Each module 702 may be configured to receive input power at the input terminals from a panel 700, and may be configured to provide output power at the output terminals. The power provided by the plurality of modules 702 may be combined between a power bus and a ground bus. In the illustrative embodiment of FIG. 7a , the output terminals of each module 702 are coupled in parallel between the power bus and the ground bus. Each module may apply Maximum Power Point Tracking (MPPT) to an associated panel 700, which may be used to extract increased power (e.g., at or about a maximum power) from the panel.

A load 750 may be coupled between the power bus and the ground bus, and may receive power generated by panels 700. In some embodiments, load 750 may comprise a DC/AC inverter. In some embodiments, load 750 may comprise a DC or an AC combiner box, one or more safety devices (e.g. one or more fuses, residual current devices, relays, disconnect switches). In some embodiments, load 750 may include a monitoring device, for example, one or more sensors configured to measure parameters (e.g. voltage, current, power, temperature and/or irradiance) and a communication device (e.g. wires or wireless) for transmitting and/or receiving messages, commands and/or data. Controller 704 may be coupled to load 750. In some embodiments, controller 704 may be a controller integrated in a DC/AC inverter, and may be implemented using an analog circuit, microprocessor, Digital Signal Processor (DSP), Application-Specific Integrated Circuit (ASIC) and/or a Field Programmable Gate Array (FPGA). The controller 704 may be in communication with modules 702, using communication methods such as Power Line Communications (PLC), wireless communications (e.g., cellular communication, WiFi™, ZigBee™, Bluetooth™ or alternative protocols) and/or acoustic communications. According to some aspects, controller 704 may be the same as or similar to controller 204.

FIG. 7a illustrates a scenario in which arc 706 may occur between an output terminal of module 702 c and the power bus. Denoting the voltage between the power bus and the ground bus as Vpg, modules 702 may measure an output voltage of about Vpg, since the output terminals each module 702 may be coupled between the ground bus and the power bus. Module 702 c may measure an output voltage different from Vpg, due to the voltage drop across arc 706. In accordance with method disclosed herein, each module 702 may regularly measure the output voltage across each module 702's respective output terminals, and comparison of measured output voltages may indicate an arcing condition. In the illustrative example of FIG. 7a , each module 702 (excluding module 702 c) may measure an output voltage of about 300V, and due to the 10V voltage drop across arc 706, module 702 c may measure a voltage drop of about 310V.

In some embodiments, one or more modules 702 may measure voltage noise, and the voltage noise measurements obtained by each module 702 may be compared (e.g. by controller 704). In some embodiments, a voltage noise measurement obtained by module 702 c may be indicative of arc 706. For example, if a voltage spectrum measured by module 702 c comprises significant high-frequency components at a magnitude not found in other voltage measurements, one or more processes or steps disclosed herein may determine that the measurement may be indicative of an arcing condition at or near module 702 c.

Reference is now made to FIG. 7b , which illustrates a method 711 for detecting an arc according to one embodiment. In some embodiments, method 711 may be carried out by a controller similar to or the same as controller 704 of FIG. 7b . In some embodiments, method 711 may be carried out by a master controller featured by a module 702. For illustrative purposes, method 711 will be described as carried out by controller 704. Steps 712-714 may be similar to or the same as steps 602-604, respectively, of method 601. At step 715, the controller (e.g. 704) carrying out method 711 may compare voltage measurements received at step 714 to one another. At step 715, the controller 704 may determine whether a measurement received from a module is different (e.g., a voltage measurement differing by more than 50 mV, 500 mV or more than 1V from the other measurements, or a voltage noise measurement differing by tens of millivolts from other voltage noise measurements). According to some aspects the voltage difference may be compared to some threshold value, which may be set by the controller or some other device. According to some aspects this threshold may be a substantial difference between voltage measurements. According to some aspects, this threshold may be a ratio of voltages. For example, if the voltage difference is twice as large as the lower voltage measurement (corresponding to a threshold ratio of two), or ten times as large as the lower voltage measurement (corresponding to a threshold ratio of ten), or if the voltage difference is equal to the lower voltage measurement (corresponding to a threshold ratio of one), the voltage difference may be considered to be greater than the threshold. If at step 716 a determination is made that an arcing condition is unlikely, the process may proceed to step 718 where the controller 704 may save the measurements received at step 714 to memory. The controller 704 carrying out process 711 may return to step 712, such as after a period of time (e.g., five minutes) has elapsed, for a new execution of method 711. In some embodiments, when past measurements might not have been used for reference, the process may proceed directly from step 716 back to step 712.

If at step 716 it is determined that an arcing condition may be present (e.g., when a voltage measurement is substantially different from other voltage measurements), the process may proceed to step 717, which may be similar to step 609 of method 601, and may set an alarm condition. In some embodiments, the controller may repeat method 711 and only proceed to step 717 if additional repetitions indicate an arcing condition (e.g., to reduce the risk of “false alarms”).

In some embodiments, measurements logged at step 718 may be used for reference during future executions of method 711. For example, a first module 702 may consistently provide an output voltage measurement which differs from the other modules' output voltage (e.g., due to a faulty sensor or to a lossy element such as a damaged wire). Steps 715 and 716 may be calibrated to account for a constant or predictable measurement difference, and step 716 may be adapted to trigger step 717 if a measurement difference continuously changes (e.g., increases) over time.

Reference is now made to FIG. 8a , which illustrates circuitry 811 such as circuitry which may be found in a photovoltaic power device 802, according to one or more aspects. Photovoltaic power device 802 may be used as, similar to, or may be module 202 of FIG. 2 and FIG. 5a and/or module 702 of FIG. 7a . In some embodiments, circuitry 811 may include power converter 801. Power converter 801 may comprise a direct current-direct current (DC/DC) converter such as a charge pump, buck, boost, buck/boost, buck+boost, Cuk, Flyback, and/or forward converter. In some embodiments, power converter 801 may comprise a direct current—alternating current (DC/AC) converter (also known as an inverter), such a micro-inverter. In some embodiments, circuitry 811 may include Maximum Power Point Tracking (MPPT) circuit 803, configured to extract increased power (e.g., at or about a maximum power) from a power source (e.g., a solar panel, solar cell, etc.) the power device is coupled to. In some embodiments, power converter 801 may include MPPT functionality. Circuitry 811 may further comprise controller 804 such as an analog circuit, microprocessor, Digital Signal Processor (DSP), Application-Specific Integrated Circuit (ASIC) and/or a Field Programmable Gate Array (FPGA). Controller 804 may be similar to or the same as controller 204 of FIG. 2, and may be similar to or the same as a control device used to control modules 202 of FIG. 2.

Still referring to FIG. 8a , controller 804 may control and/or communicate with other elements of circuitry 811 over common bus 810. In some embodiments, circuitry 811 may include circuitry and/or sensors/sensor interfaces 805 configured to measure parameters directly or receive measured parameters from connected sensors and/or sensor interfaces 805 configured to measure parameters on, at, or near the power source. These parameters may include the voltage and/or current output by the power source and/or the power output by the power source, and the like. In some embodiments the power source may be a PV module, and a sensor or sensor interface 805 may measure or may receive measurements of the irradiance received by the module and/or the temperature on, at, or near the module. In some embodiments, circuitry and/or sensors/sensor interfaces 805 may be configured to measure parameters directly or receive measured parameters from connected sensors and/or sensor interfaces 805 configured to measure parameters on or near the output of PV power device 802. These parameters may include the voltage and/or current output by PV power device 802 and/or the power output by PV power device 802.

Still referring to FIG. 8a , in some embodiments, circuitry 811 may include communication device 806, configured to transmit and/or receive data and/or commands from other devices. Communication device 806 may communicate using Power Line Communication (PLC) technology, acoustic communication technology or wireless technologies such as ZigBee™, Wi-Fi™, Bluetooth™, cellular communication or other wireless methods. In some embodiments, circuitry 811 may include memory device 809, for logging measurements taken by sensor(s)/sensor interfaces 805 to store code, operational protocols or other operating information. Memory device 809 may be flash, Electrically Erasable Programmable Read-Only Memory (EEPROM), Random Access Memory (RAM), Solid State Devices (SSD) or other types of appropriate memory devices.

Still referring to FIG. 8a , in some embodiments, circuitry 811 may include safety devices 807 (e.g., fuses, circuit breakers and Residual Current Detectors). Safety devices 807 may be passive or active. For example, safety devices 807 may comprise one or more passive fuses disposed within circuitry 811 and designed to melt when a certain current flows through it, disconnecting part of circuitry 811 to avoid damage. In some embodiments, safety devices 807 may comprise active disconnect switches, configured to receive commands from a controller (e.g., controller 804, or an external controller) to disconnect portions of circuitry 811, or configured to disconnect portions of circuitry 811 in response to a measurement measured by a sensor (e.g., a measurement measured by sensors/sensor interfaces 805). In some embodiments, circuitry 811 may comprise auxiliary power unit 808, configured to receive power from a power source coupled to circuitry 811, and output power suitable for operating other circuitry components (e.g., controller 804, communication device 806, etc.). Communication, electrical coupling and/or data-sharing between the various components of circuitry 811 may be carried out over common bus 810.

According to some embodiments, controller 804 may be configured to carry out process 611 of FIG. 6b . According to some embodiments, sensor/sensor interfaces 805 may be configured to measure the output voltage of PV power device 802 at step 613 of process 611. According to some embodiments, communication device 806 may be configured to carry out steps 612, 615 and/or 616 of process 611 by transmitting or receiving messages from a coupled communication device, and relaying received instructions to controller 804. In some embodiments, communication device 806 may be configured to carry out step 554 of processor 500 of FIG. 5c . In some embodiments, controller 804 may be configured to function as a “master controller” and to carry out processor 601 of FIG. 6a , processor 711 of FIG. 7b , and steps 552, 556, 558 and (along with communication device 806) 560 of method 500 of FIG. 5 c.

Circuitry 811 might comprise a portion of the components depicted in FIG. 8a . For example, in some embodiments, PV power device 802 may be a monitoring and/or safety device, which might not include power conversion and/or MPPT functionality (i.e., circuitry 811 might not comprise power converter 801 and/or MPPT circuit 803). In some embodiments, PV power device 802 may comprise power conversion and/or MPPT functionality, but might not comprise one or more communication features (i.e., circuitry 811 might not comprise communication device 806. For example, controller 804 may be configured to disconnect circuitry 811 from a PV string in response to detecting an arcing condition, e.g., without receiving a communication from other power devices).

In some embodiments, PV power device 802 and/or one or more components of circuitry 811 may be integrated into a photovoltaic generator. For example, circuitry 811 may be integrated into a photovoltaic generator junction box. As another example, elements of circuitry 811 (e.g., power converter 801, controller 804 and/or safety devices 807) may be embedded into PV panels or other power devices.

Reference is now made to FIG. 8b , which illustrates a portion of a photovoltaic power generation system according to an embodiment. In the illustrative embodiment depicted in FIG. 8b , a plurality of PV power devices 802 (e.g., 802 a, 802 b, . . . 802 n) may be coupled to a plurality of PV generators 800 (e.g., 800 a, 800 b, . . . 800 n) to form a photovoltaic string 820. According to some aspects, one terminal of the resultant photovoltaic string 820 may be coupled to a power (e.g., direct current) bus, and the other terminal of the string 820 may be coupled to a ground bus. In some embodiments, the power and ground buses may be input to system power device 850. In some embodiments, system power device 850 may include a DC/AC inverter and may output alternating current (AC) power to a power grid, home or other destinations. In some embodiments, system power device 850 may comprise a combiner box, DC-link, transformer and/or safety disconnect circuit. For example, system power device 850 may comprise a DC combiner box for receiving DC power from a plurality of PV strings similar to or the same as 820 and outputting the combined DC power. In some embodiments, system power device 850 may be coupled to a plurality of parallel-connected PV strings, and may include a fuse coupled to each PV string for overcurrent protection, and/or one or more disconnect switches for disconnecting one or more PV strings. In some embodiments, system power device 850 may comprise a Rapid Shutdown circuit, configured to rapidly reduce an input voltage to system power device 850 in response to a potentially unsafe condition (e.g., detecting an arc, or an islanding condition). In some embodiments, system power device 850 may be similar to or the same as load 250 of FIG. 2 and/or load 750 of FIG. 7 a.

In some embodiments, photovoltaic (PV) power device 802 a may comprise a power converter 801 a using a variation of a Buck+Boost DC/DC converter. Power converter 801 a may include a circuit having two input terminals, denoted Vin and common, and two output terminals which output the same voltage Vout. The output voltage is in relation to the common terminal. The circuit may include an input capacitor Cin coupled between the common terminal and the Vin terminal, an output capacitor coupled between the common terminal and the Vout terminals. The circuit may include a first central point and a second central point used for reference. The circuit may include a plurality of switches (e.g., MOSFET transistors) Q1, Q2, Q3 and Q4 with Q1 connected between Vin and the first central point, and Q2 connected between the common terminal and the first central point. Q3 may be connected between the Vout terminal and the second central point, and Q4 may be connected between the common terminal and the second central point. The circuit may further include inductor L coupled between the two central points.

The operation of the Buck+Boost DC/DC converter in PV power device 802 a may be variously configured. For example, if an output voltage lower than the input voltage is desired, Q3 may be statically ON, Q4 may be statically OFF, and with Q1 and Q2 being PWM-switched in a complementary manner to one another, the circuit is temporarily equivalent to a Buck converter and the input voltage is bucked. If an output voltage higher than the input voltage is desired, Q1 may be statically ON, Q2 may be statically OFF, and with Q3 and Q4 being PWM-switched in a complementary manner to one another, the input voltage is boosted. Staggering the switching of switches Q1 and Q2, the circuit may convert the input voltage Vin to output voltage Vout. If current is input to the circuit by the Vin and common terminals, and the voltage drop across capacitors Cin and Cout are about constant voltages Vin and Vout respectively, the currents input to the circuit are combined at inductor L to form an inductor current which is equal to the sum of the current input at the Vin and common terminals. The inductor current may be output by the pair of output terminals Vout. In some embodiments, more than two Vout terminals may be utilized to split the output current into more than two portions. In some embodiments, a single output terminal may be included, and system designers may split the output terminal externally (i.e., outside of the PV power device circuit), if desired.

In alternative embodiments, power converter 801 a may be modified or configured (e.g., by removing switches Q3 and Q4 and connecting the Vout terminals directly to the second central point) to be a regular Buck converter, or may be modified or configured (e.g., by removing switches Q1 and Q2 and connecting the Vin terminal directly to the first central point) to be a regular Boost converter.

Arranging a PV string in a manner similar to PV string 820 may provide several benefits. For example, by routing string current through two current paths, each current path carrying a portion of the total string current, cabling costs associated with arranging string 820 may be reduced (e.g., because conductors provided along with PV generators 800 may be utilized to carry part of the total string current). As a second example, by directly coupling an output of a first PV power device (e.g., 802 a) to a common terminal of a second PV power device (e.g., 802 b) such that a PV generator (e.g., 800 b) is coupled between the first and second PV power devices, the first and second PV power devices may be configured to carry out point-to-point power line communications (PTPPLC) and/or may determine (e.g., by detecting magnitudes and waveforms of a current flowing along the conduction path between the first and second PV power devices) that the first and second power devices may be adjacent to each other, potentially assisting with localization and mapping of PV power generation systems. Additional advantages disclosed herein include improved arc detection and localization capabilities using reduced-impedance voltage loops provided by the arrangement of PV string 820.

A first Vout terminal of PV power device 802 a may be coupled to a negative output of PV generator 800 b at connection point 1 (denoted CP1). A second Vout terminal of PV power device 802 a may be coupled to the common terminal of PV power device 802 b at connection point 3 (denoted CP3). A positive output of PV generator 800 b may be coupled to the Vin terminal of PV power device 802 b at connection point 2 (denoted CP2).

At the ground bus end of PV string 820, PV generator 800 a may be coupled to the ground bus at connection point 4 (denoted CP4). At the power bus end of PV string 820, PV power device 800 n may be coupled to the ground bus at connection point 5 (denoted CP5). For notational convenience, connection points which are not connected to the ground or power buses (e.g., connection points CP1, CP2 and CP3) will be referred to as “middle connection points”, or MCPs, and connection points which are connected to the group or power buses (e.g., connection points CP4 and CP5) will be referred to as “end connection points”, or ECPs.

While arcing can occur at nearly any location in a photovoltaic system, connection points may be particularly susceptible to arcing due to the risk of a faulty connection and/or ingress of dirt or humidity. By arranging a PV string similarly to PV string 820, sensors disposed in PV power devices 802 (e.g., sensor(s)/sensor interfaces 805 of FIG. 8a ) may detect the arcing condition by monitoring a voltage across two terminals of PV power device 802, the voltage being part of a reduced voltage loop.

Reference is now made to FIG. 8c , which illustrates a portion of a photovoltaic power generation system according to an illustrative embodiment. PV string 820, PV generators 800, PV power devices 802 and system power device 850 may be the same as the corresponding elements of FIG. 8b . First voltage loop 881 may comprise a voltage at the input of system power device 850 (denoted V850), a plurality of voltages across connection points at terminals of PV generators 800 (e.g., CP4, CP1, CP2), a plurality of voltages across PV generators 800, denoted V800, and a plurality of voltages across PV power devices 802 (i.e., a voltage between a Vout terminal and the Vin terminal of a PV power device 802). According to Kirchhoff's Voltage Law (KVL), first voltage loop 881 may be described according to Eq. 10, which follows:

$\begin{matrix} {{V_{dc} + \underset{\underset{\alpha}{︸}}{\sum\limits_{i = 1}^{N}V_{800,i}} + \underset{\underset{\beta}{︸}}{\sum\limits_{i = 1}^{N}\left( {V_{{out},{802i}} - V_{{in},{802i}}} \right)} + \underset{\underset{\gamma}{︸}}{\sum\limits_{{CP} \in {MCP}}^{\;}V_{CP}} + V_{{CP}\; 4} + V_{{{CP}\; 5}\;}} = 0} & {{Eq}.\mspace{14mu} 10} \end{matrix}$ where α denotes the summed voltages of PV generators 800, β denotes the summed Vin-to-Vout voltages of PV power devices 802, and γ denotes the summed voltages across the MCPs, i.e., across connection points between a PV generator 800 and a PV power device 802 (e.g., CP1, CP2). Voltage V850 may be monitored (e.g., measured), and the input and output voltage of PV power devices (i.e., V_(out,802) and V_(in,802i)) may be similarly monitored. Under normal (i.e., non-arcing) operating conditions, connection-point voltages may be about zero and voltages V850, V_(out,802) and V_(in,802i) may change at low-frequency or not at all (i.e., DC voltages). Under arcing conditions, an arc may inject high-frequency voltage components into a component of first voltage loop 881 (for example, if an arc is present at CP2, the voltage Vcp2 may include high-frequency components). To maintain a total voltage of zero across first voltage loop 881 (i.e., as to not violate Eq. 10), the remaining voltages featured in Eq. 10 may (e.g., the voltages across one or more of PV power devices 802 and/or system power device 850) may comprise negative high-frequency components, i.e., high-frequency voltage components having the opposite polarity compared to the high-frequency voltage components across the arc). The negative high-frequency voltage components may be detectable by sensors coupled to PV power devices 802, PV generators 800 and/or system power device 850. For example, a voltage sensor coupled to the inputs of system power device 850 may measure V850, and may be configured to raise an alarm or take corrective action in response to a V850 voltage measurement including high-frequency components (e.g., above 1 kHz) at an amplitude of over 10 mV, which may indicate an arcing condition.

In some embodiments, voltage sensors coupled to PV power devices 802 and/or system power device 850 may be dual-purpose. For example, communication device 806 of FIG. 8a may be a Power Line Communications (PLC) device configured to carry out Frequency Shift Keying (FSK) and may comprise a voltage sensor configured to measure high-frequency voltage components. Voltage components measured at certain information bands of high frequencies may be decoded for information, and voltage components measured at noise bands of high frequencies may be determined to be indicative of an arcing condition. For example, a first frequency band between 55 kHz-65 kHz, a second frequency band between 75 kHz-80 kHz and a third frequency band between 85 kHz-91 kHz may all be monitored for information signals. A fourth frequency band between 100 kHz-120 kHz may be monitored for voltage noise indicating an arcing condition.

In some embodiments, certain frequency bands may be associated with or may correspond to voltage noise that might not be indicative of an arcing condition. For example, an arc detection circuit (such as disclosed herein) may be coupled to a DC/DC converter or a DC/AC converter which may comprise one or more switches that may switch (i.e., operate, etc.) at a high frequency. The switching of the switches at a high frequency may cause voltage noise at the switching frequency and multiples thereof. For example, a converter switching one or more switches at 19 kHz may generate voltage noise at 19 kHz, 38 kHz, 57 kHz, etc. To reduce the risk of determining a false-positive arcing condition, in some embodiments, a frequency band for monitoring for an arcing condition or that may indicate an arcing condition may be selected or identified. Doing this may avoid one or more frequencies that may contain voltage noise which might not be indicative of an arcing condition (e.g., a switching frequency, etc.).

In some embodiments, a select frequency or group of select frequencies may be used for monitoring voltage noise indicating an arcing condition. The select frequency or selected frequencies may correspond to a frequency at which an impedance of a voltage loop may be reduced. For example, the total impedance of voltage loop 881 may be lowest (due to resonating capacitive and inductive elements comprising voltage loop 881) at 10 kHz. In this case, a voltage component corresponding to 10 kHz may be measured for an arc indication, or a voltage component corresponding to between 5 kHz and 20 kHz (i.e., twice and half of the low-impedance frequency) may be measured for an arc indication. In some embodiments, a loop impedance may be adjusted (e.g., by connecting adjustable capacitive and/or inductive elements) to resonate at a selected frequency, thereby improving detection of a voltage component corresponding to the selected frequency.

In some embodiments, additional voltage (or other parameter) sensing circuits may be added and configured for measuring high-frequency voltage components. For example, voltage-sensing circuits (e.g., voltage-sensing inductor circuits) may be serially coupled to input or output terminals of PV power devices, system power devices and/or photovoltaic generators, and may be configured to measure high-frequency voltage components at the input or output terminals.

Still referring to FIG. 8c , a second voltage loop 880 may comprise a voltage across a PV generator (e.g., 800 b), voltages across two MCPs (e.g., CP1 and CP2), a voltage across a connection point between two PV power devices (e.g., 802 a and 802 b), and a voltage between two terminals of a PV power device (e.g., the Vin-to-common voltage of PV power device 802 b). A plurality of voltage loops similar to voltage loop 880 may exist in a PV string 820; a similar voltage loop may be defined with regard to each PV generator in PV string 820. A Kirchhoffs current law (KCL) equation may represent voltage loop 880 according to Eq. 11, which follows: V ₈₀₀+(V _(common,802) −V _(in,802))+V _(CP1) +V _(CP2) −V _(CP3)=0

Under normal operating conditions (i.e., no arc), voltages Vcp1, Vcp2 and Vcp3 may be about zero, and Eq. 11 may reduce to Eq. 12, which follows: V ₈₀₀+(V _(common,802) −V _(in,802))=0⇒ V ₈₀₀ =V _(in,802) −V _(common,802) The voltage V_(in,802)−V_(common,802) may be continuously monitored by a voltage sensor, which may be disposed at, near, or within a PV power device 802 a. In case of an arc at one of the connection points within voltage loop 880, high frequency voltage components may be measured at the input of a PV power device 802 (e.g., 802 b), and in response, an alarm may be raised. In some embodiments, a voltage may be monitored across a communication device disposed at an input or output terminal of a PV power device 802. Under normal operating conditions, a sensor may detect and/or decode voltage components at one or more frequencies that may correspond to information signal frequencies. According to some aspects, a sensor may detect and/or decode voltage components at one or more frequencies that might not corresponding to information signal frequencies, which may be indicative of an arcing condition.

An advantage which may be realized in accordance with embodiments disclosed herein may be a reduced loop impedance of second voltage loop 880. According to some aspects, voltage sensors may be disposed at, near, or between one or more terminals of PV power devices 802 and may be configured to detect high-frequency voltage components which may be substantially larger (i.e., have a higher magnitude) than high-frequency voltage components measured within a larger loop comprising a higher loop impedance. The increased magnitude of high-frequency voltage components may facilitate early detection of arcing condition, and may enable a faster response and increased safety.

An additional advantage may include fast localization of the arc. For example, if an arc occurs at CP1, high-frequency voltage components may be detected at a first, high magnitude at PV power device 802 b (which may be part of voltage loop 880), and at a second, reduced magnitude by additional PV power devices (e.g., PV power devices 802 a, 802 n, which may be part of voltage loop 881). Comparing magnitudes of measured high-frequency voltage components may indicate that PV power device may have measured larger high-frequency voltage components, which may indicate that an arc may have occurred at or in close proximity to PV power device 802 b.

Yet another advantage of the arrangement of string 820 may be provision of a reduced-impedance loop for one or more or all connection points. In some conventional power systems, a substantial number of connection points associated with PV power devices might not be part of reduced-impedance voltage loops, potentially increasing detection time of arcing conditions. In an arrangement according to string 820, a portion of or all connection points (e.g., with the exception of connection point CP5) may be part of at least one reduced-impedance voltage loop, which may reduce the time to detect an arc at any given connection point, and may provide a method for determining a location of an arcing condition.

According to some aspects, if an arc occurs at a location other than a connection point (e.g., at the power bus, the ground bus or at conductors disposed in PV string 820, etc.), the arc may inject high-frequency voltage components which may affect voltage measurements taken at locations within first voltage loop 881 and/or within second voltage loop 880. Depending on the location of the arc, an increased magnitude of high-frequency voltage components may be measured. For example, if an arc occurs at a conductor disposed between CP1 and PV generator 800 b, an increased high-frequency voltage magnitude may be measured by PV power device 802 b. As another example, if an arc occurs at CP4, an increased high-frequency voltage magnitude may be measured by PV power device 802 a. High frequency voltage magnitudes may include voltage magnitudes at a frequency substantially above a grid frequency, for example, 200 Hz, 1 kHz, 5 kHz, 20 kHz, 100 kHz or higher. As yet another example, if an arc occurs at the ground bus, at the power bus, or at CP4, an increased high-frequency voltage magnitude might not be measured by any PV power device.

Reference is now made to FIG. 8d , which illustrates a process 840 for detecting an arc according to some aspects. Process 840 may be carried out by one or more devices (e.g., controller 704, etc.) coupled to a PV power device (e.g., controller 804 of FIG. 8a , coupled to PV power device 802) and/or a controller coupled to a system power device (e.g., system power device 850 of FIG. 8c ).

At step 841, a voltage may be measured at an input to the power device comprising the controller. For example, a voltage may be measured between input terminals or in series with an input or an output terminal of a PV power device.

At step 842, the controller may determine whether the voltage measurement obtained at step 841 comprises high-frequency components which may above a threshold. The threshold may correspond to a voltage level which is above a voltage level which likely corresponds to “normal” or typical (e.g. non-arcing) system operation. The threshold may be, as illustrative numerical examples, 10 mV or 100 mV, or some other value. As another example, the threshold may be a voltage measured at another frequency band, or at another point in coupled circuity. For example, a group of voltage measurements may be measured at a plurality of high frequencies, with the threshold being set as the difference in voltage between the greatest two of the voltage measurements. As another example, the threshold may be a ratio of voltage differences. For example, if a voltage level at a first high frequency is twice the magnitude of a voltage level at a second high frequency (corresponding to a threshold ratio of two), or one hundred thousand times the magnitude of a voltage level at a second high frequency (corresponding to a threshold ratio of one hundred thousand), the voltage difference may be considered to be greater than the threshold. As yet another example, a threshold may be set with respect to a low frequency voltage. For example, a DC voltage may be measured, and a threshold for high-frequency voltage components may be set at, for example, 2% of the value of the DC voltage.

If no such voltage components above a threshold are detected, the controller may return to step 841, and after a period of time has elapsed (e.g., seconds or minutes), restart process 840 or may return to a previous step.

If, at step 842, high-frequency voltage components above the threshold are detected, the process 840 may proceed to step 843 and determine whether the voltage components are located at frequency bands which may be used for communication. In embodiments where information might not be modulated as high-frequency voltage signals, the process 840 may proceed from step 842 directly to step 845.

If, at step 843, the controller determines that the high-frequency voltage components correspond to modulated information (e.g. a power-line-communication message comprising parameter measurements, instructions, or other information), the controller may proceed to step 844. At step 844, the controller may decode the voltage measurement to determine any information contained in the voltage measurement. The process 840 may then return to step 841.

If, at step 843, the controller determines that the high-frequency voltage components might not correspond to modulated information (e.g. the controller determines that the high-frequency voltage components may correspond to noise)), the process 840 may proceed to step 845, and the controller may set an alarm condition. Step 845 may be similar to or the same as step 408 of FIG. 4, step 528 of FIG. 5d , step 609 of FIG. 6a , and/or step 717 of FIG. 7 b.

In an illustrative embodiment, step 845 may include determining a location of an arc and transmitting localization information to wired and/or wireless network(s)/Internet/Intranet, and/or any number of end user device(s) such as a computer, smart phone, tablet and/or other devices such as servers which may be located at a network operations center and/or power generation monitoring center. Determining a location of an arc may comprise comparing voltage measurements measured by a plurality of PV power devices in a string and determining that an arc is likely present in the proximity of a PV power device which measured a high-frequency voltage component which is larger than the components measured by other PV power devices.

In some embodiments, process 840 may be carried out by a controller device coupled to a local PV power device (e.g. modules 702 of FIG. 7a ) and may include determining a location of an arc may comprise comparing measured high-frequency voltage components to a threshold. The controller may be configured to determine that the arc is adjacent to the local PV power device if the measured high-frequency voltage components are above the threshold. In some embodiments, several PV power device controllers may carry out process 840 simultaneously or sequentially, where the aggregated results of each process 840 execution may be considered by a master controller configured to set an alarm condition if more than one of the PV power device controllers determines than an arcing condition may be present.

Reference is now made to FIG. 9, which shows a photovoltaic (PV) system according to illustrative embodiments. PV system 901 may comprise a plurality of PV strings 920, each PV string 920 coupled to a string device 910, with a plurality of string devices 910 coupled in series or in parallel between a ground bus and a power bus. Each of PV strings 920 may comprise a plurality of serially-connected PV generators 900. PV generators 900 may be similar to or the same as PV panels 200 of FIG. 2, PV panels 700 of FIG. 7A and/or PV generators 800 of FIG. 8B. PV generators 900 may comprise one or more photovoltaic cells(s), module(s), substring(s), panel(s) or shingle(s). In some embodiments, PV generators 900 may be replaced by direct current (DC) batteries or alternative direct current or alternating current (AC) power sources.

A safety device 902 may be coupled at various locations in PV strings 920. For example, in some embodiments (e.g. the embodiment shown in FIG. 9), a safety device 902 may be disposed between each pair of PV generators 900. In some embodiments a safety device 902 may be disposed between groups of more than one serially-connected PV generators 900.

In some embodiments, safety devices 902 may comprise sensors/sensor interfaces for measuring electrical or thermal parameters (e.g. current, voltage, power, temperature, irradiance etc.). In some embodiments, safety devices 902 may comprise switches for disconnecting PV generators 900 in case of a potential safety condition and control/driver circuits for controlling the switches. In some embodiments, safety devices 902 may comprise arc-detection circuits configured to monitor electrical parameters (e.g. current, voltage, power) and analyze the electrical parameters to determine if an arcing condition is present. In some embodiments, safety devices 902 may comprise a wired or wireless communication device for transmitting and/or receiving measurements and/or messages.

String devices 910 may be similar to module 202 of FIG. 2, power module 702 of FIG. 7A and/or power module 802 of FIG. 8a , String devices 910 may comprise one or more of communication device 806, memory device 809, power converter 801, auxiliary power unit 808, sensor/sensor interface(s) 805, controller 804, MPPT circuit 803 and safety devices 807.

In some embodiments, a plurality of string devices 910 may be coupled in parallel between the ground bus and the power bus, as shown in FIG. 9. In some embodiments, a plurality of string devices 910 may be coupled in series between the ground bus and the power bus. In some embodiments, a plurality of string devices 910 may be coupled in a series-parallel arrangement between the ground bus and the power bus. In some embodiments, a plurality of string devices 910 may be housed by a single enclosure having multiple inputs for multiple PV strings.

Safety regulations may define a maximum allowable voltage between the ground bus and any other voltage point in PV system 901, during both regular operating conditions and during potentially unsafe conditions (e.g. a fire, grid outage, an islanding condition, arcing and the like). Similarly, safety regulations may define a maximum allowable voltage between any two voltage points in PV system 901. In some scenarios, an unsafe condition in PV system 901 may require disconnecting or short-circuiting one or more of the PV generators 900 in a PV string 920 or one or more of string devices 910.

In some embodiments, a string device 910 may respond to a potentially unsafe system condition by limiting the voltage across a PV string 920 or between the power bus and the ground bus. For example, string device 910 may comprise a converter configured to regulate a voltage of about 60V across each PV string 920 in case of a potentially unsafe condition.

In some embodiments, the power and ground buses may connect to and/or be input to system power device 950. In some embodiments, system power device 950 may include a DC/AC inverter and may output alternating current (AC) power to a load, power grid, home, or other devices or destinations. In some embodiments, system power device 950 may comprise a combiner box, a transformer, and/or a safety disconnect circuit. For example, system power device 950 may comprise a DC combiner box for receiving DC power from a plurality of PV strings 920 and outputting the combined DC power. In some embodiments, system power device 950 may include a fuse coupled to string device 910 for overcurrent protection, and/or may include one or more disconnect switches for disconnecting one or more string devices 910.

In some embodiments, system power device 950 may include or be coupled to a control device and/or a communication device for controlling or communicating with one or more safety devices 902 and/or one or more string devices 910. For example, system power device 950 may comprise a control device such as a microprocessor, Digital Signal Processor (DSP) and/or a Field Programmable Gate Array (FPGA) configured to control the operation of a string device 910. In some embodiments, system power device 950 may comprise multiple interacting control devices. System power device 950 may comprise a communication device (e.g. a Power Line Communication circuit, a wireless transceiver, etc.) configured to communicate with linked communication devices included in or coupled to safety devices 902 and/or string devices 910. In some embodiments, system power device 950 may comprise both a control device and a communication device, where the control device may be configured to determine desirable modes of operation for safety devices 902 and/or string devices 910, and the communication device may be configured to transmit operational commands and/or receive reports from communication devices included in or coupled to the safety devices 902 and/or string devices 910.

System power device 950 may be may be coupled to and/or connected to any number of other devices and/or systems, such as PV systems 100 and/or 701. For example, system power device 950 may be coupled to one or more discrete and/or interconnected devices such as disconnect(s), PV cell(s)/array(s)/panels, inverter(s), micro inverter(s), PV power device(s), safety device(s), meter(s), breaker(s), AC main(s), junction box(es), camera(s), etc. In some embodiments, system power device 950 may be coupled to and/or connected to network(s)/Intranet/Internet, computing devices, smart phone devices, tablet devices, camera, one or more servers which may include data bases and/or work stations. System power device 950 may be configured for controlling the operation of components within PV system 901 and/or for controlling the interactions with other elements coupled to PV system 901.

In some embodiments, system power device 950 may respond to a potentially unsafe system condition by limiting (e.g., decreasing to a lower voltage, decreasing to zero voltage, etc.) the voltage between the power bus and the ground bus.

In some embodiments, the power and ground buses may be further coupled to energy storage devices such as batteries, flywheels, capacitors, inductors, or other devices.

In some embodiments, safety devices 902 and/or string devices 910 may be configured to detect a proximate arcing condition and to take corrective action and/or generate a signal indicative of an arcing condition to a different device. For example, a safety device 902 may detect a possible arcing condition (e.g. using a process similar to process 840 of FIG. 8d ) at a terminal of a PV generator 900, and may disconnect the PV generator 900 to prevent or reduce danger. In some embodiments, the safety device 902 may indicate and/or report the possible arcing condition to a string device 910 and/or a system power device 950 via a wired or wireless communication signal. The string device 910 and/or a system power device 950 may be configured to reduce voltage at one or more PV generators 900 or PV strings 920 or may be configured to disconnect one or more PV strings 920 to prevent or reduce danger. In some embodiments, the safety device 902 may generate (e.g., by rapid switching of a switch, etc.) a voltage and/or current noise signal indicative of an arcing condition and detectable by a string device 910.

In another example, a string device 910 may detect (e.g., using a process similar to process 840 of FIG. 8d ) an arcing condition at an input terminal of the string device 910 or at an intermediate point in a PV string 920 (e.g., between two PV generators 900). The string device 910 may take corrective action by disconnecting and/or reducing voltage across the PV string 920, and/or may transmit a signal to system power device 950 indicating the arcing condition. For example, the string device 910 may send to system power device 950 a wired or a wireless communication signal indicating the arcing condition. As another example, the string device 910 may generate a noisy voltage and/or current signal between the power bus and the ground bus. The noisy voltage or current signal may be detectable by system power device 950 and may be indicative of an arcing condition. System power device 950 may be configured to respond to a signal indicative of an arcing condition, for example, by disconnecting one or more string devices 910 or PV strings 920, or by sending a command to reduce voltage across or current through a string device 910 or a PV string 920.

The definite articles “a”, “an” is used herein, such as “an arc voltage and/or arc current”, “a load” have the meaning of “one or more” that is “one or more arc voltages and/or arc currents” or “one or more loads”.

While the embodiments of aspects of the invention has been described with respect to a limited number of examples, it will be appreciated that many variations, modifications and other applications of the invention may be made. For example, elements of measurement synchronization disclosed with regard to process 601 may be similarly applied to other processes and aspects disclosed herein. For example, steps 552-554 of process 500 depicted in FIG. 5c may make similar use of measurement and/or transmission synchronization as described with regard to FIG. 6a . As another example, process 840 may be carried out by a single controller (e.g., controller 804 of FIG. 8a ) or by several controllers acting in conjunction. As yet another example, aspects disclosed herein may be combined with other disclosed aspects. For example, step 610 described with regard to method 601 may be added to method 711, such that if step 714 of method 711 determines that all voltage measurements were not measured at about the same time, the controller executing method 711 proceeds to a step similar to step 610.

PV generators and PV panels have been used to exemplify illustrative power sources in power generation systems disclosed herein. Apparatuses and methods disclosed herein may be implemented in power generation systems comprising batteries, capacitors, supercapacitors, fuel cells, wind turbines, hydro-generators, or other power sources in addition to or instead of PV generators and/or PV panels. 

The invention claimed is:
 1. A method comprising: obtaining a voltage measurement by measuring a voltage at a terminal of a photovoltaic power device; determining one or more voltage magnitudes associated with one or more respective frequency components of the voltage measurement; and upon determining that the one or more voltage magnitudes associated with one or more respective frequency components do not correspond to modulated information and that at least one of the one or more voltage magnitudes is above a threshold, setting an alarm condition.
 2. The method of claim 1, wherein the measuring the voltage measurement at the terminal of the photovoltaic power device comprises measuring the voltage across two input terminals of the photovoltaic power device.
 3. The method of claim 1, wherein the measuring the voltage measurement at the terminal of the photovoltaic power device comprises measuring the voltage across a circuit coupled in series with an input terminal of a photovoltaic power device.
 4. The method of claim 1, wherein the measuring the voltage measurement at the terminal of the photovoltaic power device comprises measuring the voltage across a circuit coupled in series with an output terminal of a photovoltaic power device.
 5. The method of claim 1, wherein the photovoltaic power device comprises at least one of a direct current to direct current (DC/DC) converter or a DC combiner box.
 6. The method of claim 1, wherein the photovoltaic power device is integrated with a photovoltaic power generator.
 7. The method of claim 1, wherein the setting the alarm condition comprises at least one of disconnecting the photovoltaic power device from a photovoltaic string or disconnecting the photovoltaic power device from a load.
 8. The method of claim 1, wherein the setting the alarm condition comprises transmitting a message indicating a suspected arcing condition.
 9. The method of claim 8, wherein the transmitting a message comprising indicating a location of the suspected arcing condition.
 10. A method comprising: measuring, by a photovoltaic power device, a first frequency voltage component of a first voltage loop to produce a first voltage measurement; measuring a second frequency voltage component of a second voltage loop to produce a second voltage measurement; comparing the first voltage measurement to the second voltage measurement; and upon determining that the first voltage measurement has a substantially larger magnitude than a magnitude of the second voltage measurement, setting an alarm condition.
 11. The method of claim 10, wherein setting an alarm condition comprises identifying a location associated with the first voltage measurement.
 12. The method of claim 10, wherein the setting the alarm condition comprises at least one of disconnecting the photovoltaic power device from a photovoltaic string or disconnecting the photovoltaic power device from a load.
 13. The method of claim 10, wherein the first voltage loop comprises a photovoltaic power device, and wherein the second voltage loop comprises a plurality of photovoltaic power devices.
 14. The method of claim 10, wherein the first voltage loop comprises output terminals of a photovoltaic generator and an input terminal of a photovoltaic power device.
 15. The method of claim 10, wherein the second voltage loop comprises a system power device.
 16. The method of claim 15, wherein the system power device comprises a power converter.
 17. The method of claim 15, wherein the setting the alarm condition comprises disconnecting the system power device from a photovoltaic string.
 18. The method of claim 10, wherein the measuring the first frequency voltage component comprises determining a frequency corresponding to a reduced impedance at the first voltage loop.
 19. The method of claim 10, wherein the measuring the second frequency voltage component comprises determining a frequency corresponding to a reduced impedance at the second voltage loop.
 20. The method of claim 19, wherein the determined frequency is between about 5 kHz and about 20 kHz.
 21. A method for arc detection in a system including one or more photovoltaic power modules and a load coupled to the one or more photovoltaic power modules, the method for arc detection comprising: measuring voltage delivered to the load thereby producing a first measurement; measuring voltage produced by the one or more photovoltaic power modules thereby producing a second measurement; comparing the first measurement with the second measurement thereby producing a differential voltage measurement result; and upon the differential voltage measurement result being more than a threshold value, setting an alarm condition.
 22. The method of claim 21, wherein the one or more photovoltaic power modules comprise a plurality of photovoltaic power modules, and wherein the second measurement is a sum of the voltages produced by the plurality of photovoltaic power modules.
 23. The method of claim 21, wherein the setting the alarm condition comprises disconnecting the load from the one or more photovoltaic power modules.
 24. The method of claim 21, wherein the setting the alarm condition comprises transmitting a message to a user interface of a host computer indicating a suspected arcing condition.
 25. The method of claim 21, wherein the one or more photovoltaic power modules comprises at least one of a direct current to direct current (DC/DC) converter or a DC combiner box.
 26. The method of claim 21, wherein the one or more photovoltaic power modules is integrated with a photovoltaic power generator. 